When a Stranger Calls is a 1979 American psychological thriller film written and directed by Fred Walton, co-written by Steve Feke, and starring Charles Durning, Carol Kane, Colleen Dewhurst and Tony Beckley (in his final film role). Its plot follows Jill Johnson, a young woman being terrorized by a psychopathic killer while babysitting, the killer's stalking of another woman, his returning to torment Jill years later, and a detective's trying to find him. Rachel Roberts, Ron O'Neal, Carmen Argenziano, and Rutanya Alda appear in supporting roles. The film derives its story from the folk legend of "the babysitter and the man upstairs".

The film was released in the United States on September 28, 1979 by Columbia Pictures. It was commercially successful, grossing $21.4 to $25 million at the box office against a $1.5 million budget, but it received a mixed-to-negative critical reception, with many praising the opening scene and performances, and others criticizing its writing and lack of scares. It was followed by the 1993 made-for-cable sequel When a Stranger Calls Back and a remake in 2006.

The film has developed a large cult following over time because of the first 23 minutes, consistently regarded as one of the scariest openings in film history. The first 13 minutes of Wes Craven's Scream (1996) pay homage to the opening of When a Stranger Calls.