Background Suicide is a leading cause of death in young adults. Several risk factors are well known, especially those related to adult mental health. However, some risk factors may have their origin in the very beginning of life. This study examines suicide in the general Norwegian population in a life course perspective, with a main focus on early life factors. Methods In this study, several national registers were linked, supplying personal data on biological and social variables from childhood to young adult age. Participants were all Norwegians live born during the period 1967–1976, followed up through 2004. Persons who died or emigrated before the year of their 19th birthday, at which age follow-up started, were excluded. Thus, the study population comprised 610 359 persons, and the study outcome was completed suicide. Results 1406 suicides (0.23%) were recorded, the risk being four times higher in men than in women. Suicide risk factors included not being firstborn (adjusted HR in men and women (95% CIs): 1.19 (1.05 to 1.36) and 1.42 (1.08 to 1.88)), instability of maternal marital status during childhood, parental suicide (mainly in women), low body mass index (only investigated in men), low education and indications of severe mental illness. Conclusions Suicide in young adults may be rooted in early childhood, and the effect is likely to act through several mechanisms, some of which may be linked to the composition and stability of the parental home. A life course perspective may add to our understanding of suicide.