The animal apparently hit the glass outside the facility, triggering the automatic doors, the Dallas Morning News reported.
"He came down the hallway and just kind of slid in the room," Beverly McCoy. McCoy, an X-ray technician, told WFAA.
McCoy told the television station that she was with a child when she heard a loud noise outside. When she looked in the hallway, the deer was into an empty exam room after breaking off its antlers.
"He was pretty good sized," McCoy told WFAA. "I've seen them out on a farm but never in a city like this."
The staff called animal services, which tranquilized the animal and put it on a stretcher. They released the deer after it woke up.
Williams joked that the deer might have been looking for a doctor, particularly after breaking his antlers.
"It's possible, but he didn't register," she told WFAA.