Bronchiolitis obliterans organizing pneumonia (BOOP) preceding polymyositis is rare. In this report, a 40-year-old patient with fever, chillness, generalized myalgia and progressive exertional dyspnea, had bilateral interstitial infiltrates on chest radiograph. High-Resolution CT showed subpleural and peribronchial distribution of air-space consolidation. Open lung biopsy was consistent with BOOP. Prednisolone therapy led to improvement, but during tapering of prednisolone for 3 months to 30 mg, he complained of weakness of both lower legs. One month later, prednisolone was tapered to 15 mg a day, fever, chillness and generalized myalgia were recurred. He complained of weakness of both arms. The creatine kinase (CK) with MM isoenzyme, lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) were elevated. Anti-Jo1 antibody was positive. Vastus lateralis muscle biopsy was compatible wit h polymyositis. After injection of methylprednisolone for 1 week, the patient became afebrile, the dyspnea resolved, the pulmonary infiltrates decreased, and the muscle strength improved. The serum CK, LDH, AST levels declined significantly. Patients with idiopathic BOOP should have follow-up for the possible development of connective tissue disorders including polymyositis.