The 19-year-old, whose identity was not released, was struck by a 1997 Chrysler Sebring as he rode near the intersection of Straight Path and Little East Neck Road at 8:40 p.m. Wednesday, police said.
The driver of the Sebring, identified only as a 23-year-old woman from Copiague, also was taken to Good Samaritan.
Police said she was injured when the car struck a tree after the collision with the bicyclist. She was in stable condition Thursday, police said.
No charges were filed in the accident. Police said the car was impounded for a routine safety check after the crash.