The Vancouver Family Survey collected data on the personalities, peers, and family domains of family members in 473 biological families and 128 adoptive families living in the Greater Vancouver area. Extensive family data were obtained from multiple family members, and a new measure of the addiction prone personality developed by Barnes et al. (2000) was used. Each respondent was asked if he/she had ever used marijuana or hash, cocaine or crack, LSD, speed, or heroin. Those who reported using marijuana once a week or more were categorized as "heavy" marijuana users. "Heavy" marijuana users constituted 12.6 percent of the sample. Findings from a series of regression analyses suggested that the family, personality, and peer domains all contributed significantly in predicting "heavy" marijuana use. The father's alcoholism and peer illicit drug use had direct relationships with heavy marijuana use. Higher levels of life problems were also associated with heavy marijuana use. Overall, the analysis suggests a model of mediated effects in which the family environment is predictive of the addiction prone personality trait; this trait in turn predicts peer drug use. The effects of the father's alcoholism on heavy marijuana use remains as a direct effect. Longitudinal research is required to confirm the proposed causal sequence of these effects. 5 tables, 1 figure, and 32 references