99 patients with a partial-thickness rotator cuff tear or rotator cuff tendinopathy were randomized to injection therapy with either a platelet rich plasma injection or corticosteroid injection. Patients were assessed for outcome on a visual analog scale for pain, the Western Ontario Rotator Cuff Index, the American Shoulder and Elbow Surgeons (ASES) score, and incidence of patients who progressed to operative treatment. Results demonstrated significantly greater reduction in pain after 12 weeks in the PRP group, but no significant differences between groups for improvement in WORC score or ASES score, or in the rate of patients who progressed to operative treatment.