Mindy Sterling / Clarnella
Rachel Winfree / Rose
Rance Howard / Elderly Timekeeper
Jeremy Howard / Drew Lou Who
T.J. Thyne / Stu Lou Who
Lacey Kohl / Christina Whoterberry
Nadja Pionilla / Junie
Jim Meskimen / Officer Wholihan
Michael Dahlen / Customer
David Costabile / Biker Who
Mary Stein / Miss Rue Who
James Ritz / Crazy Mose
Deep Roy / Post Office Clerk
Jessica Sara / Sophie
Mason Lucero / Who Boy
Ben Bookbinder / 8-Year-Old Augustus Maywho
Michaela Gallo / Who Schoolgirl
Landry Allbright / 8-Year-Old Martha May Whovier
Reid Kirchenbauer / 8-Year-Old Whobris /  Kid
Rebecca Chace / Shopper
Suzanne Krull / Shopper
Steve Kehela / Shopper
Lillias White / Shopper
Rain Pryor / Shopper
John Alexander / Shopper
Kevin Isola / Tree Trimmer
Gavin Grazer / Yodeler
Walter Franks / Clerk
Verne Troyer / Band Member
Clayton Martinez / Cook
Q'orianka Kilcher / Little Choir Member
Caroline Williams / Tiny Who Woman
John Short / Tiny Who Man
Grainger Esch / Near Miss Who
Eva Burkley / Pudding Chef
Rick Baker / Puppeteer
Bill Sturgeon / Puppeteer
Mark Setrakian / Puppeteer
Jurgen Heimann / Puppeteer
Tim Blaney / Puppeteer
Bryce Dallas Howard / Surprised Who (as Bryce Howard)
Charles Croughwell / Balloon Who
Frank Welker / Max the Dog (voice)
Jack Angel / Santa Claus
Rachel Bailit / Sexy Whoville Nurse
Dean Chambers / Who
Paul Eiding / Echo
Mindy Ferguson / Sexy Blonde Who
Heather Lea Gerdes / Whoville Choir
Linda Harmon / Whoville Choir
Richard Steven Horvitz / Grinch's Answering Machine (voice)
Ron Howard / Whoville Townsperson
Seth Adam Jones / Hugh Who
Tommy Karlsen / Additional Voices (voice)
Allie McCall / Noelie
Christopher Metas / Who
Ann Mills / Shopper
Sloane Momsen / Little Girl Dreaming of Sugarplums
Bonnie Morgan / Pudding Head Who
Danuta Parsons / Who
Frankie Ray / Who
Ellyse Santoro / Who
Robin Kaye Shaw / Toy Lady Who

Mel Gibson / Self
Brian Grazer / Self
John Lithgow / Self
Eric Lloyd / Self

Jon Favreau / Self
Emma Forbes / Self
Dave Goelz / The Great Gonzo /  Bunsen (voice)
Karolyn Grimes / Self
Joanna Harrison / Self
Melvyn Hayes / Self
Brian Henson / Self
Amanda Holden / Self
David Huddleston / Self
Aled Jones / Self
Patsy Kensit / Self
Taylor Momsen / Self
Barry Norman / Self
Frank Oz / Miss Piggy (voice)
Jenny Powell / Self
Daryl Sabara / Self
Jason Solomons / Self
Debra Stephenson / Self
Daniel Stern / Self
Steve Whitmire / Rizzo the Rat /  Beaker (voice)

Jim McMullan / Lyle Parks
Shelby Balik / Beth Kramer
Justin Dana / Jeff Kramer
Rick Baker / Sidney
Mike Douglas / Mike Douglas