One on Top of the Other (Italian: Una sull'altra, which the English title translates accurately but without expressing twice the feminine), also known as Perversion Story, is a 1969 giallo film directed by Lucio Fulci. Written by Fulci and Roberto Gianviti, the film stars Jean Sorel, Marisa Mell, Elsa Martinelli, Alberto de Mendoza and John Ireland. The first giallo directed by Fulci, its plot concerns George Dummurrier (Sorel), an unscrupulous San Franciscan doctor who is suspected of orchestrating the death of his asthmatic wife Susan (Mell) as part of an insurance scam, despite her seeming reemergence as Monica Weston, a high-class stripper.

One on Top of the Other was filmed on location in several United States cities, including a scene filmed in San Quentin State Prison's gas chamber. The film went on to gross 869,000,000 Italian lire and has been cited as a thematic precursor to later films such as Basic Instinct and Body of Evidence.