Criminally Insane, (also known as Crazy Fat Ethel), is a 1975 horror film written and directed by Nick Millard. Shot on location in San Francisco, it was followed by a 1987 sequel titled Criminally Insane 2.

A remake, Crazy Fat Ethel, was released in 2016.

In the film, a morbidly obese mental patient is released into the custody of her grandmother, despite a past history of violence. When the grandmother tries to prevent the patient's gorging behavior, she is killed by her own granddaughter. The granddaughter proceeds to kill further victims, hiding the corpses within her grandmother's residence. Her efforts to dispose of the bodies backfire, alerting a neighbor.