diff --git a/icu4c/source/i18n/smpdtfmt.cpp b/icu4c/source/i18n/smpdtfmt.cpp
index 8a72e4f0cd..0f7cf4ee4f 100644
--- a/icu4c/source/i18n/smpdtfmt.cpp
+++ b/icu4c/source/i18n/smpdtfmt.cpp
@@ -1,6 +1,6 @@
 /*
 *******************************************************************************
-* Copyright (C) 1997-2008, International Business Machines Corporation and    *
+* Copyright (C) 1997-2009, International Business Machines Corporation and    *
 * others. All Rights Reserved.                                                *
 *******************************************************************************
 *
@@ -514,6 +514,19 @@ SimpleDateFormat::format(Calendar& cal, UnicodeString& appendTo, FieldPosition&
     pos.setBeginIndex(0);
     pos.setEndIndex(0);
 
+    Calendar *workCal = &cal;
+    TimeZone *backupTZ = NULL;
+    if (&cal != fCalendar && uprv_strcmp(cal.getType(), fCalendar->getType()) != 0) {
+        // Different calendar type
+        // We use the time and time zone from the input calendar, but
+        // do not use the input calendar for field calculation.
+        UDate t = cal.getTime(status);
+        fCalendar->setTime(t, status);
+        backupTZ = fCalendar->getTimeZone().clone();
+        fCalendar->setTimeZone(cal.getTimeZone());
+        workCal = fCalendar;
+    }
+
     UBool inQuote = FALSE;
     UChar prevCh = 0;
     int32_t count = 0;
@@ -525,7 +538,7 @@ SimpleDateFormat::format(Calendar& cal, UnicodeString& appendTo, FieldPosition&
         // Use subFormat() to format a repeated pattern character
         // when a different pattern or non-pattern character is seen
         if (ch != prevCh && count > 0) {
-            subFormat(appendTo, prevCh, count, pos, cal, status);
+            subFormat(appendTo, prevCh, count, pos, *workCal, status);
             count = 0;
         }
         if (ch == QUOTE) {
@@ -553,7 +566,12 @@ SimpleDateFormat::format(Calendar& cal, UnicodeString& appendTo, FieldPosition&
 
     // Format the last item in the pattern, if any
     if (count > 0) {
-        subFormat(appendTo, prevCh, count, pos, cal, status);
+        subFormat(appendTo, prevCh, count, pos, *workCal, status);
+    }
+
+    if (backupTZ != NULL) {
+        // Restore the original time zone
+        fCalendar->adoptTimeZone(backupTZ);
     }
 
     // and if something failed (e.g., an invalid format character), reset our FieldPosition
@@ -1337,8 +1355,10 @@ UBool SimpleDateFormat::isNumeric(UChar formatChar, int32_t count) {
 void
 SimpleDateFormat::parse(const UnicodeString& text, Calendar& cal, ParsePosition& parsePos) const
 {
+    UErrorCode status = U_ZERO_ERROR;
     int32_t pos = parsePos.getIndex();
     int32_t start = pos;
+
     UBool ambiguousYear[] = { FALSE };
     int32_t count = 0;
 
@@ -1357,6 +1377,21 @@ SimpleDateFormat::parse(const UnicodeString& text, Calendar& cal, ParsePosition&
 
     const UnicodeString numericFormatChars(NUMERIC_FORMAT_CHARS);
 
+    TimeZone *backupTZ = NULL;
+    Calendar *workCal = &cal;
+    if (&cal != fCalendar && uprv_strcmp(cal.getType(), fCalendar->getType()) != 0) {
+        // Different calendar type
+        // We use the time/zone from the input calendar, but
+        // do not use the input calendar for field calculation.
+        fCalendar->setTime(cal.getTime(status),status);
+        if (U_FAILURE(status)) {
+            goto ExitParse;
+        }
+        backupTZ = fCalendar->getTimeZone().clone();
+        fCalendar->setTimeZone(cal.getTimeZone());
+        workCal = fCalendar;
+    }
+
     for (int32_t i=0; i<fPattern.length(); ++i) {
         UChar ch = fPattern.charAt(i);
 
@@ -1422,14 +1457,13 @@ SimpleDateFormat::parse(const UnicodeString& text, Calendar& cal, ParsePosition&
                 if (fieldPat == abutPat) {
                     count -= abutPass++;
                     if (count == 0) {
-                        parsePos.setIndex(start);
-                        parsePos.setErrorIndex(pos);
-                        return;
+                        status = U_PARSE_ERROR;
+                        goto ExitParse;
                     }
                 }
 
                 pos = subParse(text, pos, ch, count,
-                               TRUE, FALSE, ambiguousYear, cal);
+                               TRUE, FALSE, ambiguousYear, *workCal);
 
                 // If the parse fails anywhere in the run, back up to the
                 // start of the run and retry.
@@ -1443,15 +1477,14 @@ SimpleDateFormat::parse(const UnicodeString& text, Calendar& cal, ParsePosition&
             // Handle non-numeric fields and non-abutting numeric
             // fields.
             else {
-                int32_t s = pos;
-                pos = subParse(text, pos, ch, count,
-                               FALSE, TRUE, ambiguousYear, cal);
+                int32_t s = subParse(text, pos, ch, count,
+                               FALSE, TRUE, ambiguousYear, *workCal);
 
-                if (pos < 0) {
-                    parsePos.setErrorIndex(s);
-                    parsePos.setIndex(start);
-                    return;
+                if (s < 0) {
+                    status = U_PARSE_ERROR;
+                    goto ExitParse;
                 }
+                pos = s;
             }
         }
 
@@ -1504,9 +1537,8 @@ SimpleDateFormat::parse(const UnicodeString& text, Calendar& cal, ParsePosition&
             }
 
             // We fall through to this point if the match fails
-            parsePos.setIndex(start);
-            parsePos.setErrorIndex(pos);
-            return;
+            status = U_PARSE_ERROR;
+            goto ExitParse;
         }
     }
 
@@ -1538,7 +1570,6 @@ SimpleDateFormat::parse(const UnicodeString& text, Calendar& cal, ParsePosition&
     // when the two-digit year is equal to the start year, and thus might fall at the
     // front or the back of the default century.  This only works because we adjust
     // the year correctly to start with in other cases -- see subParse().
-    UErrorCode status = U_ZERO_ERROR;
     if (ambiguousYear[0] || tztype != TZTYPE_UNK) // If this is true then the two-digit year == the default start year
     {
         // We need a copy of the fields, and we need to avoid triggering a call to
@@ -1671,13 +1702,25 @@ SimpleDateFormat::parse(const UnicodeString& text, Calendar& cal, ParsePosition&
             delete copy;
         }
     }
-ExitParse: 
+ExitParse:
+    // Set the parsed result if local calendar is used
+    // instead of the input calendar
+    if (U_SUCCESS(status) && workCal != &cal) {
+        cal.setTimeZone(workCal->getTimeZone());
+        cal.setTime(workCal->getTime(status), status);
+    }
+
+    // Restore the original time zone if required
+    if (backupTZ != NULL) {
+        fCalendar->adoptTimeZone(backupTZ);
+    }
+
     // If any Calendar calls failed, we pretend that we
     // couldn't parse the string, when in reality this isn't quite accurate--
     // we did parse it; the Calendar calls just failed.
     if (U_FAILURE(status)) { 
         parsePos.setErrorIndex(pos);
-        parsePos.setIndex(start); 
+        parsePos.setIndex(start);
     }
 }
 
diff --git a/icu4c/source/i18n/unicode/datefmt.h b/icu4c/source/i18n/unicode/datefmt.h
index 5b91ac1f08..e4d5f99a0b 100644
--- a/icu4c/source/i18n/unicode/datefmt.h
+++ b/icu4c/source/i18n/unicode/datefmt.h
@@ -1,6 +1,6 @@
 /*
  ********************************************************************************
- *   Copyright (C) 1997-2008, International Business Machines
+ *   Copyright (C) 1997-2009, International Business Machines
  *   Corporation and others.  All Rights Reserved.
  ********************************************************************************
  *
@@ -245,7 +245,11 @@ public:
      * occurence of the timezone pattern character 'z'.
      *
      * @param cal           Calendar set to the date and time to be formatted
-     *                      into a date/time string.
+     *                      into a date/time string.  When the calendar type is
+     *                      different from the internal calendar held by this
+     *                      DateFormat instance, the date and the time zone will
+     *                      be inherited from the input calendar, but other calendar
+     *                      field values will be calculated by the internal calendar.
      * @param appendTo      Output parameter to receive result.
      *                      Result is appended to existing contents.
      * @param fieldPosition On input: an alignment field, if desired (see examples above)
@@ -342,7 +346,12 @@ public:
      *
      * @param text  The date/time string to be parsed
      * @param cal   a Calendar set to the date and time to be formatted
-     *              into a date/time string.
+     *              into a date/time string.  When the calendar type
+     *              is different from the internal calendar held by this
+     *              DateFormat instance, calendar field values will be
+     *              parsed based on the internal calendar, then the result
+     *              (time in milliseconds and time zone) will be set in
+     *              this calendar.
      * @param pos   On input, the position at which to start parsing; on
      *              output, the position at which parsing terminated, or the
      *              start position if the parse failed.
diff --git a/icu4c/source/test/intltest/dtfmttst.cpp b/icu4c/source/test/intltest/dtfmttst.cpp
index 67ed619eb7..3564264f78 100644
--- a/icu4c/source/test/intltest/dtfmttst.cpp
+++ b/icu4c/source/test/intltest/dtfmttst.cpp
@@ -1,6 +1,6 @@
 /********************************************************************
  * COPYRIGHT: 
- * Copyright (c) 1997-2008, International Business Machines Corporation and
+ * Copyright (c) 1997-2009, International Business Machines Corporation and
  * others. All Rights Reserved.
  ********************************************************************/
  
@@ -74,9 +74,10 @@ void DateFormatTest::runIndexedTest( int32_t index, UBool exec, const char* &nam
         TESTCASE(34,TestRelativeClone);
         TESTCASE(35,TestHostClone);
         TESTCASE(36,TestTimeZoneDisplayName);
+        TESTCASE(37,TestRoundtripWithCalendar);
         /*
-        TESTCASE(37,TestRelativeError);
-        TESTCASE(38,TestRelativeOther);
+        TESTCASE(38,TestRelativeError);
+        TESTCASE(39,TestRelativeOther);
         */
         default: name = ""; break;
     }
@@ -2898,6 +2899,128 @@ void DateFormatTest::TestTimeZoneDisplayName()
     delete cal;
 }
 
+void DateFormatTest::TestRoundtripWithCalendar(void) {
+    UErrorCode status = U_ZERO_ERROR;
+
+    TimeZone *tz = TimeZone::createTimeZone("Europe/Paris");
+    TimeZone *gmt = TimeZone::createTimeZone("Etc/GMT");
+
+    Calendar *calendars[] = {
+        Calendar::createInstance(*tz, Locale("und@calendar=gregorian"), status),
+        Calendar::createInstance(*tz, Locale("und@calendar=buddhist"), status),
+//        Calendar::createInstance(*tz, Locale("und@calendar=hebrew"), status),
+        Calendar::createInstance(*tz, Locale("und@calendar=islamic"), status),
+        Calendar::createInstance(*tz, Locale("und@calendar=japanese"), status),
+        NULL
+    };
+    if (U_FAILURE(status)) {
+        errln("Failed to initialize calendars");
+        for (int i = 0; calendars[i] != NULL; i++) {
+            delete calendars[i];
+        }
+        return;
+    }
+
+    //FIXME The formatters commented out below are currently failing because of
+    // the calendar calculation problem reported by #6691
+
+    // The order of test formatters must match the order of calendars above.
+    DateFormat *formatters[] = {
+        DateFormat::createDateTimeInstance(DateFormat::kFull, DateFormat::kFull, Locale("en_US")), //calendar=gregorian
+        DateFormat::createDateTimeInstance(DateFormat::kFull, DateFormat::kFull, Locale("th_TH")), //calendar=buddhist
+//        DateFormat::createDateTimeInstance(DateFormat::kFull, DateFormat::kFull, Locale("he_IL@calendar=hebrew")),
+        DateFormat::createDateTimeInstance(DateFormat::kFull, DateFormat::kFull, Locale("ar_EG@calendar=islamic")),
+//        DateFormat::createDateTimeInstance(DateFormat::kFull, DateFormat::kFull, Locale("ja_JP@calendar=japanese")),
+        NULL
+    };
+
+    UDate d = Calendar::getNow();
+    UnicodeString buf;
+    FieldPosition fpos;
+    ParsePosition ppos;
+
+    for (int i = 0; formatters[i] != NULL; i++) {
+        buf.remove();
+        fpos.setBeginIndex(0);
+        fpos.setEndIndex(0);
+        calendars[i]->setTime(d, status);
+
+        // Normal case output - the given calendar matches the calendar
+        // used by the formatter
+        formatters[i]->format(*calendars[i], buf, fpos);
+        UnicodeString refStr(buf);
+
+        for (int j = 0; calendars[j] != NULL; j++) {
+            if (j == i) {
+                continue;
+            }
+            buf.remove();
+            fpos.setBeginIndex(0);
+            fpos.setEndIndex(0);
+            calendars[j]->setTime(d, status);
+
+            // Even the different calendar type is specified,
+            // we should get the same result.
+            formatters[i]->format(*calendars[j], buf, fpos);
+            if (refStr != buf) {
+                errln((UnicodeString)"FAIL: Different format result with a different calendar for the same time -"
+                        + "\n Reference calendar type=" + calendars[i]->getType()
+                        + "\n Another calendar type=" + calendars[j]->getType()
+                        + "\n Expected result=" + refStr
+                        + "\n Actual result=" + buf);
+            }
+        }
+
+        calendars[i]->setTimeZone(*gmt);
+        calendars[i]->clear();
+        ppos.setErrorIndex(-1);
+        ppos.setIndex(0);
+
+        // Normal case parse result - the given calendar matches the calendar
+        // used by the formatter
+        formatters[i]->parse(refStr, *calendars[i], ppos);
+
+        for (int j = 0; calendars[j] != NULL; j++) {
+            if (j == i) {
+                continue;
+            }
+            calendars[j]->setTimeZone(*gmt);
+            calendars[j]->clear();
+            ppos.setErrorIndex(-1);
+            ppos.setIndex(0);
+
+            // Even the different calendar type is specified,
+            // we should get the same time and time zone.
+            formatters[i]->parse(refStr, *calendars[j], ppos);
+            if (calendars[i]->getTime(status) != calendars[j]->getTime(status)
+                || calendars[i]->getTimeZone() != calendars[j]->getTimeZone()) {
+                UnicodeString tzid;
+                errln((UnicodeString)"FAIL: Different parse result with a different calendar for the same string -"
+                        + "\n Reference calendar type=" + calendars[i]->getType()
+                        + "\n Another calendar type=" + calendars[j]->getType()
+                        + "\n Date string=" + refStr
+                        + "\n Expected time=" + calendars[i]->getTime(status)
+                        + "\n Expected time zone=" + calendars[i]->getTimeZone().getID(tzid)
+                        + "\n Actual time=" + calendars[j]->getTime(status)
+                        + "\n Actual time zone=" + calendars[j]->getTimeZone().getID(tzid));
+            }
+        }
+        if (U_FAILURE(status)) {
+            errln((UnicodeString)"FAIL: " + u_errorName(status));
+            break;
+        }
+    }
+
+    delete tz;
+    delete gmt;
+    for (int i = 0; calendars[i] != NULL; i++) {
+        delete calendars[i];
+    }
+    for (int i = 0; formatters[i] != NULL; i++) {
+        delete formatters[i];
+    }
+}
+
 /*
 void DateFormatTest::TestRelativeError(void)
 {
diff --git a/icu4c/source/test/intltest/dtfmttst.h b/icu4c/source/test/intltest/dtfmttst.h
index 091c459786..f39a277167 100644
--- a/icu4c/source/test/intltest/dtfmttst.h
+++ b/icu4c/source/test/intltest/dtfmttst.h
@@ -1,6 +1,6 @@
 /********************************************************************
  * COPYRIGHT: 
- * Copyright (c) 1997-2007, International Business Machines Corporation and
+ * Copyright (c) 1997-2009, International Business Machines Corporation and
  * others. All Rights Reserved.
  ********************************************************************/
 
@@ -185,12 +185,15 @@ public:
     
     void TestHostClone(void);
 
+    void TestTimeZoneDisplayName(void);
+
+    void TestRoundtripWithCalendar(void);
+
 public:
     /***
      * Test Relative Dates
      */
      void TestRelative(void);
-     void TestTimeZoneDisplayName(void);
 /*   void TestRelativeError(void);
      void TestRelativeOther(void);
 */