Background. The aim of this study was to examine the linkages between suicidal ideation and attempt in adolescence and subsequent suicidal behaviours and mental health in young adulthood.

Method. Data were gathered during the course of a 25-year longitudinal study of a birth cohort of 1265 New Zealand children. The information collected included: (a) measures of suicidal thoughts and attempts in adolescence (<18 years); (b) measures of suicidal ideation, suicide attempt, major depression, anxiety disorders, and substance use disorders in young adulthood (18–25 years); and (c) measures of childhood and family background, individual characteristics, and mental disorders in adolescence.

Results. After statistical adjustment for confounding factors, suicide attempt in adolescence was associated with increased risks of subsequent suicidal ideation (OR 5·7) suicide attempt (OR 17·8) and major depression (OR 1·5). Those reporting suicidal ideation without suicide attempt showed moderate increases in risks of later suicidal ideation (OR 2·5), suicide attempt (OR 2·0) and major depression (OR 1·6). In addition, there was evidence of an interactive relationship in which suicidal behaviour in adolescence was associated with increased risks of later substance use disorders in females but not males.

Conclusions. Young people reporting suicidal ideation or making a suicide attempt are an at-risk population for subsequent suicidal behaviour and depression. Further research is needed into the reasons for suicidal adolescent females being at greater risk of later substance use disorder.