PURPOSE: Younger age is a risk factor for worse pain outcomes following breast cancer surgery, yet little is known about how younger women's psychological state may contribute to their pain experience. Using prospectively collected longitudinal data from a surgical cohort, we examined whether early postoperative psychological distress at 2 weeks mediated the association between younger age and subsequent worse pain-related functioning 3 months after surgery. METHODS: Patients (N = 159) were recruited before breast cancer surgery into this longitudinal cohort study. Age at time of surgery, psychological distress (anxiety, depression, and sleep disturbance) assessed 2 weeks postoperatively, and impact of surgical pain on cognitive/emotional functioning and physical functioning assessed 3 months postoperatively were used for analysis. RESULTS: Younger age was associated with greater depression, anxiety, and sleep disturbance 2 weeks postoperatively. Younger age was also associated with greater ratings of pain impacting cognitive/emotional functioning and physical functioning 3 months postoperatively. The association between younger age and worse cognitive/emotional impact of pain was mediated by greater anxiety and sleep disturbance. Similarly, the association between younger age and worse physical impact of pain was mediated by greater sleep disturbance. CONCLUSION: The degree of anxiety and sleep disturbance that occur early after breast surgery may contribute to greater chronic pain-related functional disability among younger patients. Anxiety and sleep disturbance are modifiable with behavioral interventions, making them potential perioperative targets to improve long-term outcomes in young breast cancer survivors.