Little is known about the influences of peers on the sexual activity of adolescents in sub-Saharan Africa. Better understanding of these issues could lead to more effective interventions promoting sexual and reproductive health. Using two waves survey data from adolescents (n=1275) in two towns in southeastern Ghana, we examined age, gender, and community differences in peer group characteristics. We also examine prospective associations between peer group characteristics and self-reported sexual initiation, multiple partnerships, and lack of consistent condom use with most recent partner over a 20-month follow-up period. Gender differences in peer context variables were small. Affiliation with antisocial peers and perceived peer norms favoring sex increased the odds of transition to first sex. Having more friends increased the odds of accruing multiple new sexual partners among younger respondents. Among males, perceived peer norms favoring sex increased the odds of accruing multiple partners. No peer context variables were significantly associated with condom use with most recent partner. We discuss the implications of these findings for adolescent sexual and reproductive health intervention strategies in sub-Saharan Africa.