ABSTRACT. Objective: This study evaluated a gender-specific, computer-mediated intervention program to prevent underage drinking among early adolescent girls. Method: Study participants were adolescent girls and their mothers from New York, New Jersey, and Connecticut. Participants completed pretests online and were randomly divided between intervention and control arms. Intervention-arm girls and their mothers interacted with a computer program aimed to enhance motherdaughter relationships and to teach girls skills for managing confl ict, resisting media infl uences, refusing alcohol and drugs, and correcting peer norms about underage drinking, smoking, and drug use. After intervention, all participants (control and intervention) completed posttest and follow-up measurements. Results: Two months following program delivery and relative to control-arm participants, intervention-arm girls and mothers had improved their mother-daughter communication skills and their perceptions and applications of parental monitoring and rulesetting relative to girls' alcohol use. Also at follow-up, intervention-arm girls had improved their confl ict management and alcohol use-refusal skills; reported healthier normative beliefs about underage drinking; demonstrated greater self-effi cacy about their ability to avoid underage drinking; reported less alcohol consumption in the past 7 days, 30 days, and year; and expressed lower intentions to drink as adults. Conclusions: Study fi ndings modestly support the viability of a mother-daughter, computer-mediated program to prevent underage drinking among adolescent girls. The data have implications for the further development of genderspecifi c approaches to combat increases in alcohol and other substance use among American girls. (J. Stud. Alcohol Drugs 70: [70][71][72][73][74][75][76][77] 2009)