Unofficially, he retired after Muppets In Space in 1999.

He's almost 70 years old and has enjoyed a long and noteworthy career both with and beyond the Muppets.

Death at a Funeral, the remake of Death at a Funeral, the list goes on and on.

Frank Oz even did the "Little Shop of Horrors" remake in the late 80s with Rick Moranis. I'll give him a pass, I think Eric Jacobsen (the guy who replaced Frank Oz on all of his characters) is doing a passable job with them, although his Fozzie in the past has sounded like a cross between Bert and Miss Piggy on a sugar rush, but that's just this anal Muppet fan's opinion.

BJ