Although marijuana is the second most commonly abused substance among adolescents, there has been sparse research focused on the family transmission of clinically significant marijuana-related behaviors, such as abuse and dependence. As such, the authors recruited adolescents from residential and day treatment programs for youths with conduct and substance abuse problems. Interviews were conducted with the adolescents and all available family members; a total of 2,546 individuals from 781 families completed the interviews, which used structured research instruments. Risk ratios of relatives of the clinical cases were calculated and compared to control measures for marijuana use, abuse, and dependence. Structural equation modeling was used to estimate correlations among spouses, siblings, and parent-offspring transmission of marijuana-related behaviors. The proportion of variance attributable to parent-offspring transmission was also estimated. Results indicated that for all three measures of marijuana-related behaviors, the risk ratios were elevated among family members of clinical probands. Estimates among family members ranged from 1.5 to 3.3 for familial correlations; 0.33 to 0.70 for spousal correlations; 0.17 to 0.30 for parent-offspring correlations; and 0.34 to 0.44 for sibling correlations. The proportion of variance attributed to parent-offspring transmission ranged from 25 percent to 44 percent. The authors concluded that familial aggregation of marijuana use, abuse, and dependence is present and significant. Among the most significant of the findings were the parent-offspring transmission of risk factors and the significant influence of sibling environmental factors for all three levels of marijuana-related behaviors. The findings hold significance for clinical treatment options and suggest that treatments which target the family as a unit would be useful in reducing marijuana use among adolescents. Tables, references