I Saw What You Did is a 1965 Universal Pictures horror/thriller motion picture starring Joan Crawford, John Ireland, Leif Erickson, Sara Lane, Andi Garrett, Sharyl Locke, Patricia Breslin, John Archer, and Joyce Meadows.

Directed and produced by William Castle, and co-produced by Dona Holloway, the script was by screenwriter William P. McGivern, based on the 1964 novel Out of the Dark by Ursula Curtiss. Original music was by Van Alexander, and Jerry Keller (title song).

The 2002 widescreen DVD release uses the title "I Saw What You Did" And I Know Who You Are! which was the original title of the film on 1965 movie posters.

Two teens, Lisa and Kim, are playing games making prank calls on the phone. But when they call Adrian Lancer who has some mental problems, and say "I saw what you did", they ignite a human time bomb. Adrian has just killed someone and thinks they saw him do it. Now he is trying to find them. Written by Brian W Martz

When two teenagers make prank phone calls to strangers, they become the target for terror when they whisper "I Saw What You Did, And I Know Who You Are!" to psychopath Steve Marek (John Ireland) who has just murdered his wife. But somebody else knows of the terrible crime that was committed that night, the killer's desperately amorous neighbour Amy Nelson (Joan Crawford). Written by Joan Crawford & William Castle

Two teenage girls occupy their time by randomly calling strangers, whispering "I saw what you did," and hanging up. When one of their victims turns out to be a man who has just murdered his wife, he thinks they witnessed the crime and sets out to find the girls and kill them. Written by Kelly