The American designer Kate Spade was found dead at her Park Avenue apartment on Tuesday, according to police officials.

The police said that Ms. Spade, 55, was discovered unresponsive at a Park Avenue apartment, where she had hanged herself. She had left a note, but the official did not comment on what it said. She was pronounced dead at the scene at 10:26 a.m.

A housekeeper found Ms. Spade in her bedroom hanging from a red scarf tied to a doorknob, the police said. She was unconscious and the housekeeper called 911.

Ms. Spade’s husband was at the scene. A police spokesman did not know the whereabouts of Ms. Spade’s daughter.

Kate Spade, one of the first of a powerful wave of female American contemporary designers in the 1990s, built a brand on the appeal of clothes and accessories that made women smile. Her cheerful non-restraint struck a chord with consumers, as did her bright prints. She herself was the embodiment of her aesthetic, with her proto-1960s bouffant, nerd glasses, and kooky grin, which masked a business mind that saw the opportunities in becoming a lifestyle brand, almost before the term officially existed.

William K. Rashbaum and Ashley Southall contributed reporting.