This study holds the promise of developing a brief, efficacious intervention to reduce marijuana use and related sexual risk-taking behavior among the large populaton of late adolescent women who are regular marijuana users. In the abscence of intervention, these women are at heightened risk of contracting HIV and other sexually transmitted infections. Therefore it is crucial to develop an intervention that will reduce their marijuana and subsequent sexual risk taking behavior. The intervention employed in this study represents a novel adaptation of interventions that are well-supported with similar populations. If the current intervention is found to be efficacious, it can be readily integrated into a variety of treatment settings, particularly other primary care settings. In addition, this study will contribute valuable information about the relationship between marijuana use and sexual risk taking behavior and about the mechanisms of change in marijuana use in late adolescent women.