As far as I can remember, this is the first horror movie I ever saw. My mom and sister were watching it on TV, and it scared the shit out of me.
I’ve always preferred David Cronenberg to David Lynch when it came to “what-the-fuck-did-I-just-watch” cinema. In fact, it’s this point exactly that makes The Brood so scary: it’s so far out there…just the idea of what’s happening will give you goosebumps and freak you out. A description of the film from Wikipedia (since I really couldn’t put it into words any better):
“The film depicts a series of murders committed by what seems at first to be a group of children. These are in fact the psychosomatic offspring of a mentally disturbed woman, whose husband fights for custody, and finally the life, of their daughter.” Terrifying, right?

This movie has it all: body horror, killer kids, and even a statement about the topic-at-the-time, Women’s Lib.