He was last seen Tuesday afternoon, walking west from the home where he was staying on Gray Street in Brentwood.
Now, Suffolk County police have issued a Silver Alert for the missing man from El Salvador — in hopes the public can help locate him.
Police said Marciano Henriquez-Paniagua, 78, was last seen leaving the Brentwood home at about 12:40 p.m.
He has been staying with relatives at that home and another home, on Milford Drive in Central Islip, but said it was not immediately clear where he was headed when he disappeared.
Police said Henriquez-Paniagua was wearing blue jeans, a red shirt and Timberland boots when he was last seen. He was not carrying identification, a cellphone or cash.
Police are asking anyone with information on the whereabouts of Henriquez-Paniagua to call 911 or the Third Squad at 631-854-8352.
The Silver Alert program allows law enforcement to share information with media outlets about individuals with special needs who have been reported missing.