Several police and U.N. security officers at the scene who spoke on condition of anonymity because they were not authorized to speak to the media said the woman showed up at work Sunday morning and apparently jumped from the 19th floor.
The official cause of death was to be determined by the medical examiner.
U.N. staff rushed to the scene and escorted investigators to the rear area of the building shortly after 8 a.m., authorities said. Security guards and investigators put up yellow tape around the body and blocked some staff from leaving the building.
Later, the body lay draped under a white sheet on the lawn behind the 39-story building overlooking the East River.
In 1982, a 57-year-old senior U.N. official who had just resigned from the Office of Financial Services and was reported to have been upset about his failing health plunged to his death from the 18th floor of the Secretariat building.