The incident happened just after 11:30 p.m. Wednesday, June 24 in Selden.
The pedestrian was walking in the roadway on Route 25, west of Highview Drive, when he was struck by an eastbound 2004 Jeep, Suffolk County Police said.
The pedestrian, whose name is being withheld pending notification of next of kin, was transported to Stony Brook University Hospital where he was pronounced dead.
The driver of the Jeep, William McLaughlin, 19, of Selden, was not injured.
The Jeep was impounded for a safety check.
Detectives are asking anyone with information about the crash to call the Sixth Squad at 631-854-8652.
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