Police said the incident happened at about 11:35 p.m. Thursday. The motorcyclist and a car, possibly a white Mitsubishi Lancer, were seen driving at speeds over 60 mph on Sunset Boulevard and Rosemont Avenue.
The motorcyclist lost control and crashed into a wall at a fire station. He was taken to Los Angeles County USC Medical Center with severe head injuries.
The driver of the Mitsubishi fled the scene eastbound on Sunset, police said. Because the driver took off, police are treating the incident as a hit and run.
The victim is described as a male Hispanic, about 20 years old. He has not been identified.
The investigation is ongoing. Anyone with information is asked to call detectives at (213) 833-3717.