Research in developmental psychology suggests that self-concept formation and mentalizing capacities, along with their neural foundations, show significant developmental change during adolescence. Perspective-taking tendencies are also believed to increase in adolescence, supporting the refinement of prosocial behavior and the demands of increasingly complex social relationships. To explore the development of, and relationship between, these processes in adolescence, early adolescent girls (N = 172) completed a measure of perspective-taking tendencies and a self-evaluation fMRI task at two waves, approximately 18 months apart (mean ages = 11.62 and 13.20, respectively). In line with our hypothesis, perspective-taking tendencies were positively associated with age. Perspective-taking tendencies were also positively associated with a more prosocial, and less antisocial, self-concept. In addition, dmPFC activity increased with age, but this did not survive correction for multiple comparisons across all mentalizing regions. Post hoc analyses also showed that an increase in perspective-taking tendencies across waves was significantly associated with activity in parts of the precuneus at wave 2. Finally, while we did not observe cross-variable coupling, our Bivariate Latent Change Score model showed that lower perspective-taking tendencies at wave 1 were associated with greater latent change in this variable (and the same was true for mean activity in mentalizing brain regions).