We examined the longitudinal pathways from marijuana use in the familial environment (parents and siblings) and non-familial environment (peers and significant other), throughout adolescence and young adulthood, to the participants' own marijuana use in their fourth decade of life (n = 586). Longitudinal pathways to marijuana use were assessed using structural equation modeling. Familial factors were mediated by non-familial factors; sibling marijuana use also had a direct effect on the participants' marijuana use. In the non-familial environment, significant other marijuana use had only a direct effect, while peer marijuana use had direct as well as indirect effects on the participants' marijuana use. Results illustrate the importance of both modeling and selection effects in contributing to marijuana use. Regarding prevention and treatment, this study suggests the need to consider aspects of familial and non-familial social environments.