A 47-year-old man presented with an eight-day history of nonproductive cough and constitutional symptoms progressing to respiratory failure. High resolution computed tomography revealed a diffuse micronodular pattern and a 'tree-in-bud' pattern in the lower lung zones. Transbronchial biopsy showed features consistent with bronchiolitis obliterans organizing pneumonia (BOOP). After an initially difficult clinical course, the patient responded well to long term treatment with corticosteroids, including improvement of air flow obstruction. This case illustrates a variant of BOOP characterized by a comparatively acute onset, a component of proliferative bronchiolitis, an obstructive rather than restrictive pattern of pulmonary function testing and good clinical response to corticosteroid therapy.