Carl Peterson(Matt Dillon), an architect, has just get married with Molly(Kate Hudson), and it seems that they're about to begin their happy life together. Everything is going fine, until Dupree(Owen Wilson), the best man and Carl's best friend, shows up to invade the couple's intimacy. Carl's disposed to help his old friend, giving him a shelter in the couch, thinking that the whole thing will be for 2 or 3 days. Despite Dupree has promised Carl that he'll look for a job the very next day, the immature and lazy bloke spend the time playing with the children from the neighborhood, or dating with a mysterious librarian girl. Molly begins to get tired of Dupree, but Carl must deal with another problem, his malevolent and overprotecting father-in-law, who has warned him that he wants his daughter keeps her maiden name and that he doesn't even think about having children with her. Apparently, Dupree has came to stay with Molly and the stressed Carl, who doesn't know how to get rid of him, becoming paranoiac because the charismatic Dupree is starting to take his place in the household..