Globally, suicide has emerged as the second leading cause of death among youth aged 10-24 years old. In order to better understand the causes of this phenomenon, we investigate the relationship between suicidal ideation and cannabis use. Our empirical analysis is based on a 30-year longitudinal study of a birth cohort. We find that intensive cannabis use - at least several times per week - leads to a higher transition rate into suicidal ideation for males. We find no evidence that suicidal ideation leads to cannabis use for either males or females.