OBJECTIVE: To examine whether the relationships between psychological factors and rehabilitation adherence after knee surgery differ as a function of age. DESIGN AND SETTING: Participants completed inventories of self-motivation, social support, athletic identity, and psychological distress before anterior cruciate ligament (ACL) reconstruction. After surgery, participants recorded their completion of home rehabilitation exercises and cryotherapy, and the sport rehabilitation professionals providing their treatment reported on the patients' attendance at, and adherence during, rehabilitation sessions. SUBJECTS: Sixty-one individuals with acute ACL tears. MEASUREMENTS: The Self-Motivation Inventory, Social Support Inventory, Athletic Identity Measurement Scale, Brief Symptom Inventory, and Sport Injury Rehabilitation Adherence Scale were used to measure self-motivation, social support, athletic identity, psychological distress, and adherence, respectively, during rehabilitation sessions. RESULTS: Hierarchic regression analyses indicated that age moderated the relationships between (1) self-motivation and home exercise completion, (2) social support and home exercise completion, (3) athletic identity and home exercise completion, and (4) athletic identity and home cryotherapy completion. CONCLUSIONS: The prospective moderating relationships for between psychological factors and indices of adherence to home-based rehabilitation activities indicate the need to consider developmental issues when examining psychological aspects of sport-injury rehabilitation.