During a 5 1/2 year period, January, 1971 through July, 1976, 128 deaths occurred in New York City. The epidemiology of prisoner deaths including suicide was examined in a large incarcerated population. Each death was categorized according to the International Classification of Diseases. The mean age of the prisoner death was 34 years. Only 3 deaths occurred among females. Ethnic distribution of these deaths was similar to the prison population. Deaths of prisoners fell into 2 categories: external causes (suicide, accidents, homicide, legal intervention) and nonviolent causes. External causes accounted for 71 deaths. The leading cause of death was suicide, accounting for 52 deaths. Suicides occurred in all time periods of incarceration. The highest rate was in the 35 to 44 year age group. History of drug or alcohol abuse was reported by 69 per cent of the suicides. One-third of the prisoners committing suicides had histories of previous attempts or previous mental hospitalizations. Except for 2 individuals, the method was hanging. For the most part, prisoners at risk for suicide exhibited a common pattern and were identifiable. During the last 2 1/2 years of the study period, deaths were reviewed by a prisoner death committee. Deficiencies of care in deaths of nonviolent causation were categorized as "provider," "corrections," or "system." The most common deficiency in care was delay in hospitalization of prisoners requiring care.