George Clooney, Julianna Margulies and Noah Wyle all launched their careers on "ER," but none of them attended Saturday's festivities to mark the show's milestone, Usmagazine,com reported.

Current hospital staff Mekhi Phifer, Linda Cardellini, Maura Tierney and John Stamos were all on hand, however, for the bash at the Cabana Club in Hollywood where photos of previous seasons' stars lined the walls, the magazine said.

A Warner Brothers Studios representative said Clooney and his co-stars were invited to the party, but could not attend because they were working out of town.