Appropriate clinical examination and imaging may lead to early diagnosis and treatment of the shoulder impingement syndrome, thus preventing progressing to a complete tear of rotator cuff. The impingement syndrome was caused by repeated entrapment and compression of supraspinatus tendon between the proximal end of humerus inferiorly, particullary its greater tuberosity. and one or m <)re component of coracoacromial arch superiorly. The purpose of this study is to critically, evaluate the result of twenty-five consecutive subacromial decompression with impingement syndrome and to assess the diagnostic accuracy of MR imaging by using oblique coronal and oblique sagittal plan. These patients were treated by arthroscopic subacromial decompression after their pains failed to improve with conservative therapy over three month. The average follow up was 25 month(range, 12 to 50). The mean age was 43 year old. The results were rated based on subjective response and the UCLA shoulder rating scale of the result. Ten patients(40%) were rated as excellent, 11patients(44%) were good. while four patients(16%) were fair. Radiologic evaluation suggested that the oblique sagittal plan of MRI can be helpful in evaluation of bony and soft-tissue structure of the coracoacromial arch and determining depth of bony resection. There were no infection or neurovascular injury. In reviewing our result, it appears that the arthroscopic subacromial decompression can be successful sugery for shoulder impingement syndrome and diagnostic accuracy of supplimentary oblique sagittal view of MRI was relatively higher than oblique coronal view alone for apprqpriate surgical plan.