Whoever Slew Auntie Roo? (U.S. title: Who Slew Auntie Roo?) is a 1971 horror-thriller film directed by Curtis Harrington and starring Shelley Winters, Mark Lester, and Sir Ralph Richardson. Based partly on the fairy tale "Hansel and Gretel", the film focuses on a demented American widow living in her husband's English manor who becomes obsessed with a young orphan girl who resembles her dead daughter.

A co-production between the United States and the United Kingdom, the film was shot at Shepperton Studios in London. Like What Ever Happened to Baby Jane?, Hush...Hush, Sweet Charlotte, What Ever Happened to Aunt Alice, and What's the Matter with Helen?, it is one of the many films in the psycho-biddy subgenre. Whoever Slew Auntie Roo? and the latter film, also starring Winters, were released on DVD as a MGM Midnite Movies Double Feature, and Winters requested that Helen's director Harrington direct the picture.