This report studies the relationship between peer-related physical activity (PA) social networks and the PA of adolescent girls. Methods: Cross-sectional, convenience sample of adolescent girls. Mixed-model linear regression analyses to identify significant correlates of self-reported PA while accounting for correlation of girls in the same school. Results: Younger girls were more active than older girls. Most activity-related peer social network items were related to PA levels. More PA with friends was significantly related to self-reported PA in multivariate analyses. Conclusions: Frequency of PA with friends was an important correlate of PA among the peer network variables for adolescent girls.