This 23-year study explored the predictive associations between empathy development in adolescence and self-reported social competencies and outcomes in adulthood. Participants were 1,527 adults aged 35 years (48.3% female). The predictor variable (adolescent empathy) was measured yearly at the ages of 12 to 16 years. The outcome variables (adult empathy, communication skills, social integration, relationship satisfaction, and conflicts in relationships) were measured at the age of 35 years. Five important results stand out. First, longitudinal measurement invariance was established for the measure of adolescent empathy. Second, empathy tended to increase during the adolescent years. Third, significant interindividual differences in level and change of adolescent empathy were found. Fourth, gender was related to level of adolescent empathy, favoring girls over boys. Fifth, not only level but also change in adolescent empathy predicted individual differences in social competencies in adulthood two decades later. These findings demonstrate that developmental processes that are relevant for adjustment reveal long-term social consequences beyond the adolescent years.