Pedersen W. Does cannabis use lead to depression and suicidal behaviours? A population-based longitudinal study. Objective: This study investigates the relationship between cannabis use and later depression, suicidal ideation and suicide attempts in a cohort of young Norwegians. Method: Data were gathered through the Young in Norway longitudinal study, in which a population-based sample of 2033 Norwegians were followed up over a 13-year period, from their early teens to their late twenties. Data were gathered on: (a) exposure to cannabis use; and (b) depression, suicide ideation and suicide attempts. In addition, information about possible confounding factors was included. Results: In early adolescence, no associations with later depression or suicidal behaviours were observed. In the sample’s twenties, we observed highly significant associations with suicide ideation and suicide attempts. When adjusting for confounders, the OR was 2.9 (95% CI 1.3–6.1) for later suicide attempts in the group who had used cannabis 11+ times during the past 12 months. Conclusion: The findings suggest that exposure to cannabis by itself does not lead to depression but that it may be associated with later suicidal thoughts and attempts.