The accident happened at One Healthy Way, the entrance to South Nassau Communities Hospital, at 10:30 p.m.
Police said the accident occurred when a 29-year-old woman, driving a 1996 Honda, turned left in front of the motorcycle to enter the hospital.
The driver of the car was treated and released, police said. Police said the motorcyclist suffered cranial fractures, a broken leg and chest cavity trauma. Neither driver was identified by police.
No charges were filed in the crash. Police impounded both vehicles for a safety check.