Five high school seniors from West Michigan are good friends: Jim Levenstein (Jason Biggs), an awkward, nerdy and sexually naïve character whose dad Noah (Eugene Levy) attempts to offer sexual advice including purchasing and giving him pornography; Chris “Oz” Ostreicher (Chris Klein), a member of the high school lacrosse team; Kevin Myers (Thomas Ian Nicholas), the nerdy leader of the group who wants to lose his virginity to his girlfriend Vicky (Tara Reid); Paul Finch (Eddie Kaye Thomas), a mochaccino-drinking sophisticate and nerd; and Steve Stifler (Seann William Scott), a raucous jock who often throws wild parties when his mother is away, and is also the only one of the five who has lost his virginity. At Kevin’s prompting, Oz, Finch, Jim, and Kevin make a pact to lose their virginities before their high school graduation after a dorky classmate, Chuck Sherman (Chris Owen), claims to have done so at a party hosted by Stifler.
Vicky later accuses Kevin of being with her only for sex, so he must try to repair his relationship with her before the upcoming prom night, when the four plan to lose their virginity. He eventually succeeds. Oz, meanwhile, joins the school jazz choir in an attempt to find a girlfriend. From a college girl he tried to seduce, Oz learns about sensitivity and that it is about asking girls questions and listening to what they say. He soon wins the attention of Heather (Mena Suvari), a girl in the choir. However, he runs into problems when Heather learns about Oz’s reputation and breaks up with him, although he manages to regain her trust when he leaves the lacrosse championship to perform a duet with her in a choir competition.
Jim, meanwhile, attempts to pursue Nadia (Shannon Elizabeth), an exchange student from Slovakia who asks Jim for help to study for an upcoming history test. After being told by Oz that third base feels like “warm apple pie”, he practices having sex with a pie, only to be caught by Noah (who lets him keep it a secret from his mother). Stifler persuades him to set up a webcam in his room so that they can all watch Nadia changing clothes. The plan suffers a hiccup, though, when Nadia discovers Jim’s pornography collection and sits half-naked on his bed to read and masturbates to it. Jim is persuaded to return to his room, where he joins Nadia, unaware that he accidentally sent the webcam link to everyone on the school list. Nadia is interested in him, but he suffers premature ejaculation twice and is unable to have sex with her. Nadia’s exchange family sees the video and sends her back home, now leaving Jim dateless for the upcoming prom and without hope of losing his virginity before high school is over.
In sheer desperation, Jim asks band camp geek Michelle Flaherty (Alyson Hannigan) to the senior prom as she is apparently the only girl at his school who did not see what happened. Finch, meanwhile, pays Vicky’s friend, Jessica (Natasha Lyonne), $200 to spread rumors around the school of his sexual prowess, hoping that it will increase his chances of success. Unfortunately, he runs into trouble when Stifler, angry that a girl turned him down for the prom because she was waiting for Finch to ask her, puts a laxative into Finch’s mochaccino. Finch, being paranoid about the lack of cleanliness in the school restrooms, and unable to go home to use the toilet as he usually does, is tricked by Stifler into using the girls’ restroom. Afterwards, he emerges humiliated before a crowd of fellow students and is also left dateless.