diff --git a/compiler/lib/implementation/date_implementation.dart b/compiler/lib/implementation/date_implementation.dart
index 649c76c2fdf..4702236e533 100644
--- a/compiler/lib/implementation/date_implementation.dart
+++ b/compiler/lib/implementation/date_implementation.dart
@@ -90,7 +90,16 @@ class DateImplementation implements Date {
   }
 
   int get weekday() {
-    throw "Unimplemented";
+    final Date unixTimeStart =
+        new Date.withTimeZone(1970, 1, 1, 0, 0, 0, 0, timeZone);
+    int msSince1970 = this.difference(unixTimeStart).inMilliseconds;
+    // Adjust the milliseconds to avoid problems with summer-time.
+    if (hours < 2) {
+      msSince1970 += 2 * Duration.MS_PER_HOUR;
+    }
+    int daysSince1970 = (msSince1970 / Duration.MS_PER_DAY).floor().toInt();
+    // 1970-1-1 was a Thursday.
+    return ((daysSince1970 + Date.THU) % Date.DAYS_IN_WEEK);
   }
 
   bool isLocalTime() {
diff --git a/runtime/lib/date.dart b/runtime/lib/date.dart
index efab0104840..0227a1e3975 100644
--- a/runtime/lib/date.dart
+++ b/runtime/lib/date.dart
@@ -170,7 +170,23 @@ class DateImplementation implements Date {
   }
 
   int get weekday() {
-    throw "Unimplemented";
+    final Date unixTimeStart =
+    new Date.withTimeZone(1970, 1, 1, 0, 0, 0, 0, timeZone);
+    int msSince1970 = this.difference(unixTimeStart).inMilliseconds;
+    // Adjust the milliseconds to avoid problems with summer-time.
+    if (hours < 2) {
+      msSince1970 += 2 * Duration.MS_PER_HOUR;
+    }
+    // Compute the floor of msSince1970 / Duration.MS_PER_DAY.
+    int daysSince1970;
+    if (msSince1970 >= 0) {
+      daysSince1970 = msSince1970 ~/ Duration.MS_PER_DAY;
+    } else {
+      daysSince1970 =
+            (msSince1970 - Duration.MS_PER_DAY + 1) ~/ Duration.MS_PER_DAY;
+    }
+    // 1970-1-1 was a Thursday.
+    return ((daysSince1970 + Date.THU) % Date.DAYS_IN_WEEK);
   }
 
   bool isLocalTime() {
diff --git a/tests/corelib/src/DateTimeTest.dart b/tests/corelib/src/DateTimeTest.dart
index 5c927402a1b..78c39760fe3 100644
--- a/tests/corelib/src/DateTimeTest.dart
+++ b/tests/corelib/src/DateTimeTest.dart
@@ -331,6 +331,36 @@ class DateTest {
     Expect.equals("2011-05-11 18:58:35.000Z", str);
   }
 
+  static void testWeekday() {
+    var d = new Date(2011, 10, 6, 0, 45, 37, 0);
+    Expect.equals(Date.THU, d.weekday);
+    d = new Date.withTimeZone(2011, 10, 6, 0, 45, 37, 0, const TimeZone.utc());
+    Expect.equals(Date.THU, d.weekday);
+    d = new Date(2011, 10, 5, 23, 45, 37, 0);
+    Expect.equals(Date.WED, d.weekday);
+    d = new Date.withTimeZone(2011, 10, 5, 23, 45, 37, 0, const TimeZone.utc());
+    Expect.equals(Date.WED, d.weekday);
+    d = new Date(1970, 1, 1, 0, 0, 0, 1);
+    Expect.equals(Date.THU, d.weekday);
+    d = new Date.withTimeZone(1970, 1, 1, 0, 0, 0, 1, const TimeZone.utc());
+    Expect.equals(Date.THU, d.weekday);
+    d = new Date.withTimeZone(1969, 12, 31, 23, 59, 59, 999,
+                              const TimeZone.utc());
+    Expect.equals(Date.WED, d.weekday);
+    d = new Date(1969, 12, 31, 23, 59, 59, 999);
+    Expect.equals(Date.WED, d.weekday);
+    d = new Date(2011, 10, 4, 23, 45, 37, 0);
+    Expect.equals(Date.TUE, d.weekday);
+    d = new Date(2011, 10, 3, 23, 45, 37, 0);
+    Expect.equals(Date.MON, d.weekday);
+    d = new Date(2011, 10, 2, 23, 45, 37, 0);
+    Expect.equals(Date.SUN, d.weekday);
+    d = new Date(2011, 10, 1, 23, 45, 37, 0);
+    Expect.equals(Date.SAT, d.weekday);
+    d = new Date(2011, 9, 30, 23, 45, 37, 0);
+    Expect.equals(Date.FRI, d.weekday);
+  }
+
   static void testMain() {
     testNow();
     testValue();
@@ -342,6 +372,7 @@ class DateTest {
     testDateStrings();
     testEquivalentYears();
     testFarAwayDates();
+    testWeekday();
   }
 }