I Know This Much Is True

Mark Ruffalo

Dominick Birdsey / Thomas Birdsey

Melissa Leo

Concettina Ipolita Tempesta 'Ma' Birdsey

Rosie O'Donnell

Lisa Sheffer

Archie Panjabi

Dr. Patel

Kathryn Hahn

Dessa Constantine

John Procaccino

Ray Birdsey

Rob Huebel

Leo

Michael Greyeyes

Ralph Drinkwater

Gabe Fazio

Shawn Tudesco / Dominick and Thomas Acting Double

Harris Yulin

Father Lavie

Bruce Greenwood

Dr. Hume

Marcello Fonte

Domenico Onofrio Tempesta

Sue Jean Kim

Dr. Yup

Michael Simon Hall

Stuart Feinstein

Gina Costigan

Mrs. O'Meara

Steven Cox

Boyfriend of Dr. Hume's Daughter

MorningStar Angeline

Nabby Drinkwater's Wife

Al Linea

Abruzzi