The so-called hard hat bandit entered the Chase Bank branch in West Babylon on Sunrise Highway at 12:51 p.m. on Wednesday.
Police say the man approached a teller, demanded cash and indicated that he had a gun.
The teller complied with the suspect's demands and gave him cash from the drawer.
The man fled and was last seen driving westbound on Sunrise Highway Service Road in an older model, tan-colored, 4-door sedan.
The suspect is described as a white male wearing an orange construction helmet, blue work coveralls and work boots.
He was also wearing glasses with black frames, black gloves, and a bandage over his right eye which was used to disguise his appearance.
He is described as being in his late 30s to early 40s, clean shaven and with a heavyset build.
Anyone with information regarding this incident is asked to call anonymously Crime Stoppers at 1-800-220-TIPS. All calls will remain confidential.