We report a 51-year-old man who presented with 3 weeks of polyarthritis with fever, nonproductive cough, bibasilar crackles, tachypnea, and hypoxia. Initial laboratory data showed an increased erythrocyte sedimentation rate, rheumatoid factor, and anti-Jo-1 antibody. Imaging studies showed bilateral lower lobe infiltrates of the lung. A transbronchial biopsy specimen revealed characteristic findings for bronchiolitis obliterans organizing pneumonia (BOOP). About 6 months later, he developed profound proximal muscle weakness with a dramatic increase in creatine phosphokinase and aldolase and a further elevation of anti-Jo-1. Muscle biopsy specimen findings were consistent with polymyositis.This represents an unusual case in which BOOP occurred at the onset of an illness initially suggestive of rheumatoid arthritis (RA). The anti-Jo-1-positivity led to close follow up and later discovery of evolution into polymyositis. BOOP can be an early feature of polymyositis as well as RA.