The incident happened in Central Islip, at the Bank of America on Wheeler Road, at around 9:30 a.m. Tuesday, Aug. 13.
Suffolk County Police said a man demanded cash and threatened violence while displaying what appeared to be a gun in his waistband.
The teller complied and the suspect fled on foot with cash. No employees or customers were injured.
Police described the suspect as Black, in his mid to late 30s, between 5-foot-10 and 6-feet tall, with a thin build and long black hair. He was wearing a burgundy flannel shirt and black pants.
Anyone with information is asked to contact Suffolk County Police at 631-852-6555 or Crime Stoppers at 1-800-200-TIPS.
Click here to follow Daily Voice Bay Shore and receive free news updates.