Credit: Gilbert Carrasquillo/FilmMagic; Steven Lawton/FilmMagic

Joan Rivers -- who's famously had her lips, breasts, nose, eyes, stomach and arms done and regularly gets Botox -- supports Heidi Montag, who got 10 plastic surgery operations in a day.

"I think she should have started sooner!" she told Monday at the NYC premiere of her documentary, Joan Rivers A Piece Of Work.

She then cracked, "I think she should have started when she was 13."

Kidding aside, Rivers, 76, says Montag, 23, "looks fine now, but she could have done it in stages."

Who should go under the knife next?

"Kate Gosselin," Rivers replied. "They should sew up that uterus!"