Background. This study examined associations between childhood circumstances, adolescent mental health and life events, and the development of suicidal behaviour in young people aged between 15 and 21 years.

Method. Data were gathered over the course of a 21-year longitudinal study of a birth cohort of 1265 children born in New Zealand. The measures collected included: (1) patterns of suicidal behaviour (ideation, attempt) (15–21 years); (2) social background, family functioning, parental and individual adjustment during childhood (0–16 years); and (3) time dynamics of mental health and stressful life events during adolescence and early adulthood (15–21 years).

Results. By the age of 21 years, 28·8% of the sample reported having thought about killing themselves and 7·5% reported having made a suicide attempt. The childhood profile of those at greatest risk of suicidal behaviour was that of a young person reared in a family environment characterized by socio-economic adversity, marital disruption, poor parent–child attachment and exposure to sexual abuse, and who as a young adolescent showed high rates of neuroticism and novelty seeking. With the exception of the socio-economic and personality measures, the effects of childhood factors were largely mediated by mental health problems and exposure to stressful life events during adolescence and early adulthood. Mental health problems including depression, anxiety disorders, substance use disorder, and to some extent conduct disorder, in addition to exposure to adverse life events, were significantly associated with the onset of suicidal behaviours.

Conclusions. Findings support a life course model of the aetiology of suicidal behaviour in which risk of developing suicidal behaviour depends on accumulative exposure to a series of social, family, personality and mental health factors.