Gender role attitudes have important implications at the individual, family, and societal levels, underscoring the importance of understanding their development. Although parents predominate in the socialization of gender role attitudes in childhood, the influence of friends increases during adolescence. In particular, cross-gender friends can provide unique insights and perspectives on another gender group, making them likely to shape gender role attitudes. However, empirical explorations of the link between gender role attitudes and cross-gender friendships have been rare. Furthermore, the few studies conducted have yielded ambiguous results and have struggled to separate the influence of cross-gender friends from a selection of such friendships based on gender role attitudes. This study addresses these limitations by using longitudinal social network models to assess the co-evolution of friendship networks and gender role attitudes among 3,194 youth (Mage = 15.2, SD = 0.67, 51% female) in German schools. The findings reveal that, after accounting for selection processes, boys with cross-gender friends develop more egalitarian gender role attitudes, while girls’ attitudes are unaffected by cross-gender friendships. These findings suggest that promoting cross-gender friendships among adolescent boys holds the potential to foster egalitarian gender role attitudes.