AIM To examine the extent of psychiatric illness amongst young people making medically serious suicide attempts and control subjects. METHOD Using a case control design, 129 young people making serious suicide attempts were contrasted with 153 randomly selected community controls on a series of measures of current and lifetime DSM-III-R diagnoses of mental disorders. RESULTS Individuals making suicide attempts were characterised by high rates of current mental disorder (89.5%), current comorbidity (54.3%), lifetime histories of psychiatric disorder (90.7%) and previous suicide attempts (52.7%). At the time of the suicide attempt, those making serious attempts had elevated rates of the following disorders: affective disorders (70.5%), substance use disorders (38.8%), anxiety disorders (14.7%), eating disorders (8.5%) and antisocial disorders (34.9%). CONCLUSIONS Young people who made medically serious suicide attempts had high rates of a range of mental disorders, and of comorbid disorders, at the time of the suicide attempt. They had high rates of lifetime histories of mental disorders and previous suicide attempts. The implications of these findings for the development of strategies to manage, treat and prevent suicidal behaviours in young people are discussed.