Discrepancies in first- (M = 14.97 years, SD = 1.82) and second-born adolescents' (M = 12.20 years, SD = 1.90 years) and their parents' perceptions of parental authority legitimacy (PAL) were examined in a longitudinal sample of 145 predominantly White, middle-class, U.S. families. Utilizing a growth curve modeling approach, changes in the discrepancies between parents' and both first- and second-born adolescents' ratings of PAL over the course of 4 years were examined separately by the social-cognitive domain of the issues (social domain theory; Smetana, 2011; Turiel, 2002). We found that discrepancies between parents and first-borns increased over time for personal and multifaceted issues, whereas discrepancies for second-born adolescents increased over socially regulated issues. Additionally, larger initial discrepancies between parents and both adolescents over socially regulated issues (i.e., moral and conventional) were associated with greater depressive symptoms, while decreases in discrepancies over time were generally associated with better adjustment outcomes but with some domain and birth order differentiation. Discussion focuses on the developmental appropriateness (or inappropriateness) of family member perception differences in authority legitimacy over the course of adolescence.