Big Brothers/Big Sisters is a national program aimed at providing mentors for disadvantaged children. This study tested whether Big Sister mentors could be trained to increase communication with their Little Sisters about sexual health issues. The study tested an intervention based on social cognitive theory in which a sexual health communication program was tested against an attention-matched control condition (bullying/peer pressure). Results showed level of self-efficacy for talking about sex increased within subjects, regardless of study condition. Big Sisters in the experimental group spent more time talking with their Little Sisters about romantic relationships as compared to those in the control at follow-up. (Contains 3 tables, 1 figure, and 2 notes.)