Polymyalgia rheumatica (PMR) is an inflammatory condition of unknown etiology characterized by diffuse pain and morning stiffness involving neck, shoulder, and pelvic girdles. To facilitate an understanding of PMR and its proper diagnosis, we evaluated clinical symptoms, laboratory data, and radiographic findings of 32 Japanese patients with it. Distal musculoskeletal manifestations were more frequently observed than had been thought before (81% of the patients), and peripheral arthritis was most common (75%). The joints most often affected were knees and wrists, and most episodes were presented as bilateral oligo- or polyarthritis. A swelling of hands was observed in 34% of the patients. Using contrast-enhanced fat suppression magnetic resonance imaging (MRI) of the shoulder, we found the evidence of subacromial and subdeltoid bursitis (100%), glenohumeral joint synovitis (93%), and biceps tenosynovitis (57%) in the PMR patients examined. Inflammatory changes in soft tissues around the joint capsule were prominent. By knee MRI, suprapatellar bursitis and joint synovitis were visualized in all cases examined, and extracapsular abnormalities were also prominent in 90% of the patients. Serum matrix metalloproteinase-3, a parameter of synovial inflammation, was significantly increased in PMR patients. Anticyclic citrullinated peptide antibody was useful for differential diagnosis between PMR and elderly onset rheumatoid arthritis. In conclusion, joint and periarticular synovitis seems to be commonly and primarily responsible for the proximal and distal musculoskeletal symptoms of PMR. The presence of the extracapsular change, probably a nonspecific extension of synovitis, can explain the severe discomfort that radiates toward the periphery. To avoid making a wrong diagnosis, we should be aware that peripheral synovitis is one of the hallmarks of PMR.