Orgasmo (Italian for "orgasm") is a 1969 giallo film co-written and directed by Umberto Lenzi and starring Carroll Baker, Lou Castel, and Colette Descombes. It follows a wealthy American socialite who finds herself preyed upon by two nefarious young siblings who indulge her with sex, drugs, and alcohol while she vacations at an Italian villa. This film helped launch the second phase of Baker's career, during which she became a regular star in Italian productions.

After its Italian premiere in February 1969, Orgasmo was released in the United States under the alternative title Paranoia later that same year. It was one of the first films to carry an X rating in the United States under the newly established Motion Picture Association film rating system, and this fact was sensationalized for its American promotional materials.

The film marked the first of four collaborations between Lenzi and actress Carroll Baker, who also starred in So Sweet... So Perverse (1969), A Quiet Place to Kill (1970) and Il coltello di ghiaccio (1972).

American socialite Catherine West arrives in Italy from New York to a flurry of journalists following the car accident death of her husband Robert, a Texas oil baron who left her his $200 million estate. She retreats to an Italian villa rented by her austere lawyer, Brian Sanders. Catherine soon meets Peter Donovan, a young American man from Boston whose car has broken down nearby. Peter manages to manipulate his way into staying with Catherine, who is initially icy toward his romantic advances. However, Peter swiftly manages to seduce her, and the two engage in a passionate affair.

Catherine travels to London to visit with her late husband's relatives to discuss property she is bequeathing to them, but finds them to be abrasive and angry with her, believing she married Robert solely for his money. Late one night, Catherine senses someone has broken into the house, but the housekeeper Teresa attributes Catherine's paranoia to her abuse of alcohol and prescription drugs. When Catherine invites Peter to stay with her for a week, his sister Eva arrives at the villa unexpectedly. Catherine enjoys the siblings' companionship and youthful vivaciousness.

During a dinner meeting with Brian, Catherine admits she is suffering from liver failure due to her alcoholism. Upon returning to the villa, Catherine finds Peter and Eva in bed together nude. She presumes the two have engaged in incest, but Peter informs Catherine that he and Eva are not blood-related, and are in fact only stepsiblings. Eva confesses that she is sexually attracted to Catherine, and the three soon engage in a series of nightly debaucherous threesomes fueled by Peter and Eva's indulging of Catherine in liquor and stimulant drugs.

One night, Catherine, disgusted with herself and in a drunken rage, orders Peter and Eva to leave the villa. They oblige, but soon return, and begin physically abusing Catherine and taking control of the house, subduing Catherine by forcing her to drink. Finding herself held hostage by the siblings, Catherine becomes increasingly desperate to escape Peter and Eva. She manages to produce a gun, with which she shoots Peter. Catherine loses consciousness due to a sedative fed to her by Eva, and awakens to find that the gun was loaded with blanks by the siblings, and that Peter was unharmed. The two bind and gag Catherine, tying her to a bed. When Brian visits the villa, Peter tells him that Catherine has descended into a depression, and has threatened to commit suicide.

Locked in her upstairs bedroom, Catherine is further tormented by the siblings, who, on one occasion serve her a live toad for dinner. The two later bring her whiskey and a large number of barbiturates, along with a falsified letter stating Brian has died in a plane crash, with the hope that Catherine will voluntarily kill herself by overdosing. Catherine manages to escape her bedroom and flees to the attic, accessing the roof of the villa. Brian arrives, and witnesses Catherine collapse over the edge of the roof, falling to the veranda below and fracturing her skull. Brian picks the injured Catherine up in his arms. The two briefly make eye contact before he ruthlessly throws her over the veranda onto the driveway below, killing her. Brian, who has conspired with the siblings to steal Catherine's fortune, produces two forged suicide notes and orders Peter to alert authorities to Catherine's staged suicide. It is revealed that Brian is in fact Peter and Eva's uncle, and had Catherine unknowingly sign documents that bequeathed her estate to the trio.