Objective: Synovitis and bursitis have been demonstrated in polymyalgia rheumatica (PMR). But myositis has been rarely reported in PMR. Magnetic resonance imaging (MRI) has been used in PMR because of its potential to localize inflamed tissues. We sought to investigate the muscular involvement in PMR. Methods: We analyzed MRI findings of shoulder and pelvic girdle of 12 patients diagnosed by Chuang`s diagnostic criteria for PMR at Kyungpook National University Hospital. Inflammations in joint, bursa and muscle were examined. Results: The male to female ratio was 1:1. Mean age at diagnosis was 64.2 years. MRI of shoulder (5 patients) showed subacromial subdeltoid bursitis (60%), synovitis of gleno-humeral joint (40%), synovitis of acromioclavicular joint (20%) and juxtaentheseal myopathy (20%). MRI of pelvis (10 patients) showed synovitis of hip joint (20%), trochanteric bursitis (30%), ischial bursitis (20%), juxtaentheseal myopathy (60%) and myopathy (20%). Overall muscular involvement rate of PMR was 58.3%. Iliopsoas and hip rotators were the most common involved muscles and hamstring, gluteus maximus, and gluteus medius were followed in order of frequency. Muscular involvement were characterized by juxtaentheseal myopathy which was defined as inflammation of muscle around the site of bone attachment and near the fascia and by patch distribution of small areas of muscle fibers. Conclusions: MRI of PMR revealed characteristic findings of juxtaentheseal myopathy in addition to bursitis and synovitis. This study suggest that juxtaentheseal myopathy in pelvis may contribute to the diffuse pain and stiffness in the pelvic girdle observed in patients with PMR at least partially.