Suffolk County Police said it happened just after 10 p.m. Friday night in Port Jefferson Station.
The victim was crossing Route 112, south of Rose Avenue, when he was struck by an unknown SUV that police believe was heading southbound.
The vehicle fled the scene.
Another vehicle traveling southbound also struck the victim. That driver remained on the scene.
The victim, who has not yet been identified by police, was pronounced dead.
Detectives are asking anyone with information on the crash to call the Major Case Unit at 631-852-6553 or call anonymously to Crime Stoppers at 1-800-220-TIPS.
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