A rash of bizarre murders in New York City seems to point to a group of grotesquely deformed vagrants living in the sewers. A courageous policeman, a photo journalist and his girlfriend, and a nutty bum, who seems to know a lot about the creatures, band together to try and determine what the creatures are and how to stop them.

"C.H.U.D." is an acronym for "Cannibalistic Humanoid Underground Dweller", but it also means "Contamination Hazard Urban Disposal", as one can (barely) read on the crates full of toxic materials.

Mrs. Monroe:
Cooper, you son of a bitch. I'm in jail. I only get one phone call. You think I wanna waste it talking to some goddamn fucking machine?

Continuity: At the end of the movie when George Cooper and the Reverend escape from the manhole, they realize that they are trying to be killed by Wilson, the supposed NRC guy. The Reverend finds Captain Bosch lying on the ground who was just shot (by Wilson) and grabs Bosch's gun from his belt. After killing Wilson, a scene is shown with the Reverend kneeling beside Bosch who still has the gun tucked in his belt.