It happened Sunday on busy South Oyster Bay Road at Hicks Avenue in Syosset.
Police say a 2002 Chevrolet Impala, driven by a 32-year-old man, struck a 15-year-old boy on a skateboard.
The boy then collided with his friend who was skateboarding with him.
The boy who was struck by the car suffered a severe head injury and was taken to North Shore Syosset Hospital where he was pronounced dead.
The other boy was taken to an area hospital by Nassau County Ambulance for treatment of a fractured ankle.
Detectives report no apparent criminality with the accident at this time.
The vehicle was impounded from the scene for brake and safety inspections.
Identification of the deceased is being withheld pending family notification.