diff -r a8abcf708255 javafx-ui-controls/src/com/sun/javafx/scene/control/skin/PopupMenuSkin.fx
--- a/javafx-ui-controls/src/com/sun/javafx/scene/control/skin/PopupMenuSkin.fx	Fri Apr 02 00:55:06 2010 -0700
+++ b/javafx-ui-controls/src/com/sun/javafx/scene/control/skin/PopupMenuSkin.fx	Tue Apr 13 15:16:18 2010 +1200
@@ -274,10 +274,23 @@
 
     override function impl_computePrefWidth(height) {
         var max = 0.0;
-        for (item in items) {
-            if (not item.visible) then continue;
-            max = Math.max(getNodePrefWidth(item), max);
+        var separatorWidth = 0.0;
+        for (item in items where item.visible) {
+            // We don't want to include the width of any Separator control in the
+            // width calculations for this menu, but we do record the width of
+            // the widest separator, so that we can handle the situation where
+            // the max variable remains 0.0.
+            if (item instanceof javafx.scene.control.Separator) {
+                separatorWidth = Math.max(getNodePrefWidth(item), separatorWidth);
+            } else {
+                max = Math.max(getNodePrefWidth(item), max);
+            }
         }
+
+        if (max <= 0.0) {
+            max = separatorWidth;
+        }
+
         return padding.left + max + padding.right;
     }
 
@@ -327,8 +340,7 @@
 
     function getContentHeight():Number {
         var h = 0.0;
-        for (item in items) {
-            if (not item.visible) then continue;
+        for (item in items where item.visible) {
             h += getNodePrefHeight(item, width);
         }
         return h;