BACKGROUND The surgical treatment of massive rotator cuff tears (RCT) is still controversial and can be based on a variety of different surgical repair methods. This study investigated the effectiveness of arthroscopic debridement or arthroscopic partial repair in patients with massive RCT. METHODS This prospective, randomized study involved forty-two patients with massive RCT (fatty infiltration stage 3 or 4) treated with either arthroscopic partial repair or arthroscopic debridement were selected to detect possible differences in functional outcome. Both groups were matched according to age and gender. Patients were examined before, and 16 +/- 3 and 24 +/- 2 months after surgery. The status of the rotator cuff repair was determined using ultrasonographic evaluation. RESULTS Regardless of the treatment group, postoperative results demonstrated highly significant improvements compared with preoperative values in most parameters. The overall Constant score in the partial repair group was superior to the outcome in the debridement group (P < 0.01, F = 8.561), according to better results in abduction (P < 0.01, F = 13.249), activity (P < 0.01, F = 21.391) and motion (P < 0.01, F = 4.967). All treatment groups had similar pain relief (P = 0.172, F = 1.802) and satisfaction, reflected in equal values of disabilities of the arm, shoulder and hand (DASH) score (P = 0.948, F = 0.004). Ultrasonography revealed structural failure of the partial rotator cuff repair in 52% at final follow-up. CONCLUSIONS During the follow-up period all patients in our series had good or satisfactory outcome after rotator cuff surgery. Regardless of high rates of structural failure of the partial rotator cuff repair, the results of arthroscopic partial rotator cuff repair demonstrated slightly better functional outcome than debridement.