There are many scenes of nudity in this movie, mostly female, but in one case male as well. This movie nevertheless gets a PG rating because the nudity is all non-sexual nudity, and it is all essential to the plot. All parts of the body are visible at one point or another except for pubic areas or genitalia, which we never see clearly.
The limit of sex in this movie is on-screen passionate kissing between the leading couple. Off-screen sex is only implied.
Young Freddie (Jason Late) pretends to drop a coin in order to sneak looks up women's skirts. Later in the movie, the grown up Freddie (John Candy) pulls the same trick.
A man reads a Penthouse magazine. (It is the June 1983 issue.) We only see the cover, on which the model is shown topless but with a rose positioned over her nipple. Several references are made to the magazine in dialogue, including a reference to lesbianism. There are other sexual innuendos in dialogue elsewhere in the film.
Madison (Daryl Hannah) runs away from the camera down a beach, naked. She walks up to Allen (Tom Hanks), kisses him on the mouth, then takes a running dive into the surf and swims away. Throughout this scene, we see her bared buttocks and legs several times. Her long hair covers most of her back and completely conceals her breasts, but it is clear she is wearing nothing.
Madison swims topless underwater in a long sequence in mermaid form, with her lower body being that of a fish. During this, we get multiple clear views of her breasts, including areolae and nipples.
Madison walks naked into a large crowd of people. We see her bare buttocks in an extended rear shot. In this shot, we get a brief glimpse of her pubic hair and genitalia from the rear, but only a knowledgeable eye sees this. We see only a brief glimpse of sideboob in this scene, as her long hair mostly covers her breasts.
Madison and Allen passionately kiss several times in public as they are making their way to his apartment. In the apartment, they kiss several more times, and at the end of the scene they are embraced and kissing on his bed. No sex is shown, but it is implied in a later scene, where they are shown in bed together.
Allen and Madison are naked in a large clear water tank. He covers his genitalia with his hands, and her lower body is covered by her fish form. We see her breasts several times, as well as a glimpse of the side of his buttocks.
In pretending to be a foreigner, Freddie (John Candy) tells another man in Swedish that he has a 12-inch penis, intending to be understood only as a non-English speaker. The ploy succeeds, with the other man being oblivious about the meaning of the statement, but for comedy purposes, this statement is typically subtitled with either forced or burned-in subtitles.