A 22-year-old man from Lethbridge is in critical condition after falling out of the back of a pick-up truck.

Lethbridge Regional Police say the man was dropped off at the hospital around 4 a.m. MT on Friday with life-threatening head injuries.

Investigators have determined the man was riding in the box of a truck when he fell out and hit his head.

The 19-year-old female driver of the truck took the man to hospital but left prior to police arriving.

The man was taken to Calgary's Foothill Hospital where he remains in critical condition.