This study tested a brief web-based, family-involvement health promotion program aimed at drug use, physical activity, and nutrition for adolescent girls, aged 10 to 12 years, who reside in public housing. Separately, girls (n = 67) and their mothers (n = 67) completed baseline measures online. Following baseline, 36 randomly assigned mother-daughter dyads jointly completed a 3-session, health promotion program online. Subsequently, all girls and mothers separately completed posttest and 5-month follow-up measures. Attrition at posttest and 5-month follow-up measures was 3% and 9%, respectively. At posttest, intervention-arm girls, relative to control-arm girls, reported greater mother-daughter communication and parental monitoring. Intervention-arm mothers reported greater mother-daughter communication and closeness as well as increased vegetable intake and physical activity. At 5-month follow-up, intervention-arm girls and mothers, relative to those in the control arm, reported greater levels of parental monitoring. Intervention-arm girls also reported greater mother-daughter communication and closeness, reduced stress, greater refusal skills, and increased fruit intake. Findings indicate the potential of a brief, web-based program to improve the health of low-income girls and their mothers.