One hundred fifty patients with full-thickness supraspinatus tendon tears were randomized to receive leukocyte-rich PRP (n=50), leukocyte-poor PRP (n=50), or no PRP (control, n=50) during arthroscopic rotator cuff repair. The primary outcome was the University of California, Los Angeles (UCLA) shoulder score at 12 months. Secondary outcomes included the American Shoulder and Elbow Surgeons (ASES) and Constant scores, visual analog scale (VAS) pain scores, range of motion (ROM), and structural integrity on MRI using Sugaya classification. Outcomes were assessed at 3, 6, and 12 months. Overall, the study showed no significant differences in the primary outcome or most secondary outcomes among the three groups at 12 months. However, the LR-PRP group had slightly better ASES scores at 3 and 6 months postoperatively. These findings suggest PRP does not offer superior long-term outcomes in arthroscopic rotator cuff repair, though LR-PRP may transiently improve short-term function.