The deadly fire raised new questions about the safety conditions at Russia's medical institutes, after a string of fires in the recent years.
The fire broke out on the partly-wooden roof and spread rapidly throughout the one-story hospital building, sources in the health ministry said. Preliminary reports said 38 people, including two female medical staff members, were killed, a news agency cited sources saying.
The emergency situations ministry said that 41 people were in the building at the time of the fire. Over 100 firefighters battled to douse the flames and twelve bodies were found from the rubble.
The country's Investigative Committee said that it had opened a criminal probe into the failure to observe fire regulatory regulations, causing multiple deaths. A nurse managed to save just two patients along with herself, sources said.
Most of the victims died in their sleep by inhaling fumes of the fire.
The Moscow region will observe mourning on Saturday.