A medical intern living at the Helmsley Medical Tower plunged to his death out of an apartment window on the Upper East Side on Friday, police said.

Police believe the 25-year-old victim, who lived alone, jumped off the 20th floor and landed on a third-floor vestibule at the building — a New York Presbyterian Hospital facility near East 70th Street and York Avenue.

A worker discovered the man around 9:20 a.m., but it is believed he jumped sometime overnight, an employee of the management agency told The Post.

“It’s a resident who jumped. A worker discovered him this morning coming in,” the employee said.

A little over 300 residents live in the upper floors at the Helmsley building, which also provides housing for guests whose loved ones require extended medical care.

The identity of the deceased is pending proper family notification, cops said.