Purpose: The purpose of this study was to analyze the possible contributing factors and surgical results of rotator cuff tears in patients younger than 40 years of age. Materials and Methods: From July, 1996 to February, 2000, twelve patients were available to participate in the study. The average age was 35 years (range, 17 to 40 years) old. Follow-up averaged eighteen months (range, 12 to 55 months). There were eleven men and one women. Each shoulder was evaluated with UCLA shoulder functional assessment, return-to-work status, return-to-sport status, and overall postoperative satisfaction. Results: After operation, eleven patients (92%) reported diminished pain relative to their preoperative level, and ten patients (83%) were improved in shoulder function. eleven patients (92%) exhibited improved strength after operation. nine patients (75%) returned to employment, and six patients (50%) returned to sports activities. Preoperative UCLA score averaged 12 and postoperative score averaged 31. Ten patients (83%) were satisfied with the outcome of their treatment. Conclusion: A traumatic event was the etiology of the rotator cuff tears in patients younger than 40 years. Results of surgical treatment in this younger group were satisfactory.