Big Brothers/Big Sisters is a national program aimed at providing adult mentors for disadvantaged children. The current study tested whether Big Sister mentors could be trained to increase communication with their Little Sisters about sexual health issues, including delay of sexual debut, pregnancy, and STDs/HIV. The study tested an intervention based on social cognitive theory, the Healthy "Little" Lives Project, in which a sexual health communication program (experimental group) was tested against an attention-matched control condition (bullying/peer pressure). It was hypothesized that Big Sisters randomly assigned to the experimental group would have higher levels of self-efficacy, more positive outcome expectancies for sex-based communication, and a greater number of conversation enactments than those in the comparison group following completion of the program session. None of the major hypotheses were supported. However, level of self-efficacy for talking about sexual health issues increased within subjects, regardless of study condition. In addition, Big Sisters in the experimental group talked for a longer amount of time with their Little Sisters about romantic relationships with boys as compared to those in the control condition at the two week follow-up. In addition, most Big Sisters who participated in the study found the program helpful and enjoyable. Possible explanations for the lack of significant effects for the intervention are discussed.