Eight fire engines and 58 firefighters and officers were called to a fire at a hospital on The Ridgeway in Enfield.
A small part of the ground floor of a two floored building was damaged by fire.
Forty five people were evacuated from hospital wards before the Brigade arrived. Seven people were treated for smoke inhalation at the scene. Fifteen people have been moved to alternative accommodation on site for the night.
The Brigade was called at 2211 and the incident was under control by 0041. Fire crews from Enfield, Southgate, Edmonton, Chingford and Barnet fire stations were at the scene.
The cause of the fire is under investigation.