A man slipped away from police custody on Thursday when officers took him to Lincoln Medical and Mental Health Center in the Bronx after he complained that his arm hurt, the police said.

The man, Kevin Lopez, 26, was arrested in the Hunts Point neighborhood of the Bronx at 8 p.m. Wednesday on charges of drug sales and resisting arrest, the police said. He told the police his left arm was injured and was taken to the hospital for X-rays in handcuffs on Thursday morning, the police said.

One officer was stationed outside of the radiology room on the first floor and another officer stood behind a protective partition inside the room, said the chief spokesman for the Police Department, Paul J. Browne. The handcuffs were removed for the X-ray.

After about 10 minutes, when the X-rays were completed, the officer came out from behind the partition, but Mr. Lopez was gone. He had apparently slipped away through a second door in the room and fled. "When the...