Charlie Babbit (Tom Cruise) is having financial woes when his father passes away. He expects to inherit the estate but is shocked to elarn that he has a brother and that the money went to that brother. He travels to the mental institution where his brother is a patient. His brother, Raymond, (Dustin Hoffman) turns out to be a savant who is a genius with numbers. Charlie takes his father's old car and his brother and starts driving across the country to his home. Along the way he finds out how difficult it can be to have his brother around. Raymond won't fly. Raymond refuses to wear any underwear except the ones purchased at K-Mart in Cincinnati. Raymond has to see Judge Wopner every day. But, he also starts realizing that he cares about his brother. He petitions the court for custody of Raymond, but finally accepts the fact that Raymond is beter off back in the home.