Five high school seniors and friends from fictional East Great Falls, Michigan: Jim Levenstein, an awkward and sexually naïve nerd whose dad offers him pornography and unwanted sexual advice; Chris "Oz" Ostreicher, overconfident star of the lacrosse team; Kevin Meyers, the calm leader of the group seeking to lose his virginity to his girlfriend Vicky; Paul Finch, a mochaccino-drinking sophisticate; and Steven Stifler, a popular but raucous jock who often throws wild parties and is the only one of the five who is not a virgin. When dorky classmate Sherman claims that he lost his virginity at a party hosted by Stifler, Kevin prompts Oz, Finch, and Jim to join him in pledging that they will no longer be virgins by their high school graduation.
Vicky accuses Kevin of wanting her only for sex and he has to repair their relationship before the senior prom, now the target day the four plan to lose their virginity. Kevin discovers an old book in the library that has been compiled by students sharing sexual tips; he shares the information with his friends and gives Vicky cunnilingus after studying tips in the book. Oz joins the school choir to find a girlfriend and learn about sensitivity. He soon gains the attention of choir girl Heather, who learns about Oz's reputation and breaks up with him. Jim pursues Nadia, a foreign exchange student from Czechoslovakia.
When Oz tells Jim that third base feels like "warm apple pie", his dad discovers him having sex with a freshly baked pie in the kitchen. At school, Nadia asks Jim to help her study, and Stifler persuades Jim to set up a webcam in his room so that they can all watch Nadia changing clothes after coming over to study following her ballet class. Nadia discovers Jim's pornography collection and while sitting half-naked on his bed, masturbates to it. Jim is persuaded to return to his room, where he joins Nadia, unaware that he has sent the webcam link to everyone on the school list. He fails to cover the webcam and he experiences premature ejaculation — twice. Nadia's sponsors see the video and send her back home, leaving Jim dateless for the prom and the laughing stock of the school.
Jim, believing school band geek Michelle is unaware of the webcam incident, asks her to the prom. Finch pays Vicky's friend, Jessica, $200 to spread the rumor of his sexual prowess, hoping that it will increase his chances of success. Stifler is turned down by a girl because she wants Finch to ask her, so he spikes Finch's mochaccino with a laxative. Stifler plays to Finch's school restroom germaphobia and has loud diarrhea in the girl's bathroom. He is humiliated by Stifler and a crowd of students. Oz leaves a lacrosse championship game to join Heather for a duet performance and the two reconcile.
At prom, Sherman's virginity conquest is revealed to be a lie and he urinates on himself in front of everyone in attendance. Jim becomes annoyed by Kevin's obsession to have them fulfill their pledge. At Stifler's post-prom party, Kevin and Vicky have sex in an upstairs bedroom. Vicky breaks up with Kevin afterwards on the belief that they will drift apart when they go to college. Oz confesses the pact to Heather and renounces it. They share a romantic night together by the lake. Jim learns that Michelle accepted his offer because she saw the "Nadia incident" and thought he was a "sure thing". Michelle then has aggressive sex with Jim. Finch meets and seduces Stifler's mom and they have sex on the pool table. Stifler later walks in on them and faints. The morning after the prom, the group discuss their successful pledge while eat breakfast at their favorite restaurant. Honoring his newfound sensitivity, Oz does not divulge to his friends whether or not he and Heather had sex. The friends then toast to the "next step".
Later, Nadia watches Jim stripping via webcam. Jim is oblivious to his father walking in, who then walks out of the room and starts dancing.
Jason Biggs as Jim
Jennifer Coolidge as Stifler's Mom
Shannon Elizabeth as Nadia
Alyson Hannigan as Michelle
Chris Klein as Oz
Clyde Kusatsu as English Teacher
Eugene Levy as Jim's Dad
Natasha Lyonne as Jessica
Thomas Ian Nicholas as Kevin
Chris Owen as Sherman
Lawrence Pressman as Coach Marshall
Tara Reid as Vicky
Seann William Scott as Stifler
Mena Suvari as Heather
Eddie Kaye Thomas as Finch
Molly Cheek as Jim's Mom
Christina Milian as Band Member
Eden Riegel as Sophomore Chick
John Cho as "Milf" Guy
Sasha Barrese as Random Cute Girl
Eric Lively as Albert
Eli Marienthal as Stifler's Younger Brother
Tara Subkoff (uncredited) as College girl
Chris Weitz (uncredited) as Male voice in porn film
Cameos
Blink-182 make a cameo appearance as the band watching Jim and Nadia during their webcast
Casey Affleck as Tom Myers
Stacy Fuson, Playmate of the Month for February 1999, appears in the crowd laughing at Finch when he exits the girls' restroom.
the first film in the American Pie series