Although there is a theoretical and empirical basis for age-related changes in adolescents' empathy and prosocial behaviors, as well as in bidirectional relationships, research examining their codevelopment is lacking. Specifically, research on the extent to which an adolescent's mean-level growth in empathy is related to parallel mean-level growth in his or her prosocial behavior is needed. This 3-year longitudinal multicohort study of adolescents (NT1 = 1,045, 52.0% girls; MageT1 = 14.67 years) conducted in France investigated the codevelopmental associations between adolescents' empathy mean-level growth and prosocial behaviors mean-level growth via parallel latent growth curve modeling. The parallel latent growth curve model indicated general mean-level increases in empathy and prosocial behaviors over time. The findings support the codevelopment of empathy and prosocial behaviors, with mean-level growth in empathy related to parallel mean-level growth of prosocial behaviors in early and middle adolescence. Importantly, both trajectories exhibited significant interindividual variability. Additionally, the initial levels of empathy were positively related to the initial levels of prosocial behaviors and vice versa. Interestingly, our results suggest that higher baseline levels of empathy are related to steeper decreases in the slope of prosocial behaviors over time and that higher baseline levels of prosocial behaviors are related to steeper decreases in the slope of empathy over time. Age- and gender-related findings were also observed. We discuss the codevelopment and developmental relationships between empathy and prosocial behaviors, the differences across age groups, and their practical implications. (PsycInfo Database Record (c) 2025 APA, all rights reserved).