The driver, a 72-year-old man, tried to leave the van and a struggle between the two ensued, police said.
Both men fell from the van, and the suspect made off with the victim's keys and wallet and drove off in the van, traveling east on Hempstead Turnpike, police said.
The driver of the van was not injured, police said.
Anyone with information can call Crime Stoppers at 800-244-8477. All calls will be kept confidential.