The suspected shooter was also wounded and was reported to be in critical condition. Delaware County District Attorney Jack Whelan told reporters he has "psychiatric issues."
The shooting occurred on the third floor of the Sister Marie Lenahan Wellness Center at Mercy-Fitzgerald Hospital. The hospital is in Darby, a Philadelphia suburb.
Whelan said the doctor apparently had a gun and shot the suspect.
"We're not exactly sure what had occurred and what might have precipitated this particular incident," Whelan said. "We do know the psychiatric connection, we have that concern, however we don't know if there was another dispute that occurred inside that room that led to these shots being fired."
The dead woman's identity was not released, pending notification of her family.
Officials said the doctor had a graze wound. He and the suspected shooter were both transported to University of Pennsylvania Hospital.
The wellness center is across the street from the hospital and connected to the main building by a pedestrian walkway. The hospital was locked down for about 90 minutes, while the wellness center remained closed late in the afternoon.