Carl Peterson (Matt Dillon) and Randy Dupree (Owen Wilson) have been friends forever. But everything changes when Carl marries Molly Thompson (Kate Hudson) and best man Dupree becomes the third wheel. Free-spirited Dupree's antics suddenly seem juvenile and Carl has to decide where his loyalty lies--with his new wife or his best friend. Still, when Carl discovers that Dupree is down on his luck--he's lost his job, his company car, and his apartment--he invites his best buddy to move in until he's back on his feet. Unfortunately, Dupree isn't exactly Molly's idea of the perfect houseguest. This perpetual bachelor is really an overgrown kid who moves in with a giant moosehead, likes to sleep in the buff, has some unpleasant hygiene issues, and treats life like one big party. Despite Dupree's inability to grow up, he has a good heart: he's just trying to find his niche and enjoy every day along the way.

To make matters worse for Molly, Carl has become a cranky workaholic since his boss, Molly's father (Michael Douglas), promoted him. Disheartened by her new husband's late hours, Molly begins to spend more time with Dupree and to see his softer side--something that even Carl has never been aware of. Carl, meanwhile, begins to resent his lackadaisical friend and to question his motives. Ultimately, it's up to Dupree to get Carl and Molly back on track. Wilson gives Dupree a puppy-dog quality that makes him immensely likable, even when he's screwing up. Dillon is surprisingly funny as the straight man in the duo, trying to balance his old life with his new responsibilities. Supporting actor Seth Rogen is a hoot as Carl and Dupree's friend, Neil, who desperately wants to be his own man but is completely under his wife's thumb.