Kieran Culkin as Jason "Igby" Slocumb Jr.
Rory Culkin as 10-year-old Igby

Claire Danes as Sookie Sapperstein

Jeff Goldblum as D. H. Banes

Bill Pullman as Jason Slocumb Sr.

Susan Sarandon as Mimi Slocumb

Ryan Phillippe as Oliver "Ollie" Slocumb

Bill Irwin as Lt. Ernest Smith

Jared Harris as Russel

Amanda Peet as Rachel, D. H. Banes's mistress

Celia Weston as Bunny, Mrs. D. H. Banes

Cynthia Nixon as Mrs. Piggee

Eric Bogosian as Mr. Nice Guy

Jim Gaffigan as Hilton manager

Gore Vidal as Catholic priest

Marion Ross as Mrs. Slocumb, Mimi's grandmother who spended days at a nursing home

L.Q. Jones as Mr. Slocumb

Keith...