BACKGROUND The age, sex, and ethnic distribution of adolescents who commit suicide is significantly different from that of the general population. The present study was designed to examine psychiatric risk factors and the relationship between them and demographic variables. METHODS A case-control, psychologic autopsy study of 120 of 170 consecutive subjects (age, <20 years) who committed suicide and 147 community age-, sex-, and ethnic-matched control subjects who had lived in the Greater New York (NY) area. RESULTS By using parent informants only, 59% of subjects who committed suicide and 23% of control subjects who met DSM-III criteria for a psychiatric diagnosis, 49% and 26%, respectively, had had symptoms for more than 3 years, and 46% and 29%, respectively, had had previous contact with a mental health professional. Best-estimate rates, based on multiple informants for these parameters, for suicides only, were 91%, 52%, and 46%, respectively. Previous attempts and mood disorder were major risks factors for both sexes; substance and/or alcohol abuse was a risk factor for males only. Mood disorder was more common in females, substance and/or alcohol abuse occurred exclusively in males (62% of 18- to 19-year-old suicides). The prevalence of a psychiatric diagnosis and, in particular, substance and/or alcohol abuse increased with age. CONCLUSIONS A limited range of diagnoses--most commonly a mood disorder alone or in combination with conduct disorder and/or substance abuse--characterizes most suicides among teenagers.