75 patients with complete supraspinatus tears were randomized to undergo arthroscopic rotator cuff repair with or without the injection of platelet-rich plasma (PRP). The purpose of this study was to compare functional and structural results between groups up to 24 months post-surgery. The UCLA score was significantly higher in the PRP group than in the control group at the 12 month follow-up, but this difference was not present at any other time point. Constant scores and VAS pain scores improved similarly in both groups throughout the follow-up period, and no significant differences in retear rates or complications were observed between groups.