The Mexican moviemaker was travelling in a vehicle with his father when they passed the scene of an accident and he saw a headless body lying in the wreckage.
The incident had a profound effect on the young Del Toro and he became obsessed with dark thoughts about death.
He tells Britain's The Times, ""I can still remember the red car passing us on the highway. My father told me, 'Those guys are crazy, they're gonna die'. Twenty minutes later we hit some traffic... then we saw the upturned car and a guy crying by the road. My father said, 'Look somewhere else'. But I didn't do that.
""The corpse was neck down with its a** exposed. It wasn't face down - its head was somewhere else, tangled up in a barbed-wire fence. After that I became slightly preoccupied: I worried a lot about death. Strangely enough it's not something I worry about now as an adult.""