Parents’ differential treatment (PDT) and their children’s appraisals of its fairness have been linked to adjustment across childhood and adolescence, primarily in Anglo American families. We extend this literature by studying Mexican-origin siblings’ appraisals of PDT fairness and jealousy toward siblings and their longitudinal links with emerging adult adjustment. Siblings’ familism values, sibling dyad gender constellation, and birth order were examined as moderators of these linkages. Participants were mothers, fathers, and two siblings from 246 Mexican-origin families who completed home interviews at three points in time across 8 years. Appraisals of mothers’ and fathers’ fairness in late adolescence (younger siblings)/emerging adulthood (older siblings) predicted siblings’ depressive symptoms 2 years later, but no relations emerged with jealousy. Familism values and sibling dyad gender constellation did not moderate these associations. Mothers’ and fathers’ differential conflict in early-/mid-adolescence predicted siblings’ risky behaviors in emerging adulthood. Discussion highlights the importance of PDT dynamics for emerging adults’ adjustment.