The study identified a subset of youth who are at risk for excessive cannabis use that may impair their life opportunities and health. Forty-seven percent of the total sample of 8,225 students from grades 7 through 12 had used cannabis in their lifetime. Under a grouping of cannabis users according to their frequency of use (“never users,” “frequent users,” or “heavy users”), male heavy cannabis users (used cannabis 10 or more times in the past 30 days) composed 14.3 percent of the boys in the total sample, who composed 50 percent of the sample. The male heavy cannabis users were more likely to be in ninth grade or higher; be Aboriginal; report poorer economic status; never feel like an outsider; frequently use alcohol and tobacco; and have lower satisfaction with family, friends, and school compared with boys who had never used cannabis. Female heavy users (8.7 percent of girls) were more likely to be in a higher grade; report poorer economic status, mental health, and academic performance; frequently use alcohol and tobacco; and have lower satisfaction with their school compared with girls who had never used cannabis. The multivariate analysis of the correlates of cannabis use found three important gender differences: school grade (for boys only); Aboriginal status (for boys only); and mental health (for girls only). These gender differences are important in planning the design and implementation of cannabis prevention or treatment programs for adolescents. 5 tables and 57 references