Sha Tin Hospital on Thursday said staff found a psychiatric patient unconscious in a ward toilet at about 10.40 am.
A hospital spokesman said the 51-year-old man had clothing coiled around his neck. He was rushed to Prince of Wales Hospital, where he was certified dead about an hour later.
Shatin Hospital has reported the case to the police, the coroner, and to the Hospital Authority. Next of kin have been informed.
An investigation will take place and a report submitted in eight weeks.