- Robin Williams
- T.S. Garp
- Mary Beth Hurt
- Helen Holm
- Glenn Close
- Jenny Fields
- John Lithgow
- Roberta Muldoon
- Hume Cronyn
- Mr. Fields
- Jessica Tandy
- Mrs. Fields
- Swoosie Kurtz
- The Hooker
- James McCall
- Young Garp
- Peter Michael Goetz
- John Wolfe
- George Ede
- Dean Bodger
- Mark Soper
- Michael Milton
- Nathan Babcock
- Duncan Garp
- Ian MacGregor
- Walt Garp
- Warren Berlinger
- Stew Percy
- Susan Browning
- Midge Percy
- Brandon Maggart
- Ernie Holm
- Jenny Wright
- Cushie
- Brenda Currin
- Pooh
- Jillian Ross
- Young Cushie
- Laurie Robyn
- Young Pooh
- Victor Magnotta
- First Coach
- Dominic A. Cecere
- Opposing Coach
- John Irving
- Referee
- Dan Goldman
- Wrestling Opponent
- Al DePippo
- Heavyweight
- Christopher Farr
- Bosworth
- Brett Littman
- Zipper Boy
- Brandon Roth
- Infant Garp
- Steven Krey
- Boy Babysitter
- Laura Kaye
- Little Jenny
- Al Cerullo
- Helicopter Pilot
- Amanda Plummer
- Ellen James
- Bette Henritze
- Woman Candidate
- Jean De Baer
- Woman Speaker
- Ron Frazier
- Stephen
- Katherine Borowitz
- Rachel
- Isabell O'Connor
- Woman with Book
- John S. Corcoran
- Man in Tree
- Tim Gallin
- Fireman
- Kate McGregor-Stewart
- Real Estate Lady
- Sabrina Lee Moore
- Babysitter
- Matthew Cowles
- Speeding Plumber
- Eve Gordon
- Marge Tallworth
- David Fields
- Infant Duncan
- Ryan Davis
- Duncan at 2 Years
- Kaiulani Lee
- Chief Ellen Jamesian
- Harris Laskawy
- Randy
- Lori Shelle
- Laurel
- Kath Reiter
- Alice
- Thomas Peter Daikos
- Flying Baby Garp
- Ron Berliner
- Guest
- Daniel Donaghy
- Baby Garp
- Linda Hamil
- Party Guest
- George Roy Hill
- Pilot
- Garett Maggart
- Kid
- Douglas Rowan
- Rally Member
- Joe Rubbo
- Wrestler
- Lee Strauss
- (uncredited)
- Mike Tremont
- Heckler
- Jean Zarzour
- Ellen Jamesian
