Younger sisters of teenage parents have elevated rates of engaging in unprotected sex. This may result from changes in parenting behavior after a sibling becomes pregnant or impregnates a partner, and be particularly pronounced for girls seeking mental health treatment. The current study examines condom use over time in 211 African-American girls recruited from outpatient psychiatric clinics. Findings indicate that having a sibling with a teenage pregnancy history predicts less consistent condom use 2 years later. After accounting for earlier condom use and mental health problems, maternal monitoring moderates condom use such that for girls with a sibling with a pregnancy history, more vigilant maternal monitoring is associated with increased condom use, while for girls with no sibling pregnancy history, maternal monitoring is unrelated to adolescents’ condom use 2 years later. Findings suggest that targeted interventions to increase maternal monitoring of high-risk teens may be beneficial for girls with a sibling history of teenage pregnancy.