The 30-year-old woman, whose name was not released, was in a room facing the FDR Drive at the hospital at 535 East 70th St. when the bullet came crashing through the window about 5:45 a.m., according to police and hospital officials.
The falling glass slashed the patient's face, the NYPD said. She was moved to a different room and treated on scene. Police recovered a copper jacketed slug at the scene, sources said.
It was not immediately clear where the bullet came from.
The eighth floor is used for for patients before and after surgery, a hospital spokeswoman said.
Police had made no arrests and were still investigating, a spokesman said.
The hospital, which was founded in 1863, has won top honors in various medical fields and performs more than 25,000 surgical procedures each year, including for the city's top athletes with the New York Knicks, New York Mets, New York Liberty and other teams, according to its website.
A hospital spokeswoman said staff are cooperating with the NYPD investigation and referred all inquires to them.