A 70 year old man presented with symptoms and laboratory findings suggestive of chlamydial pneumonia. Despite adequate antibiotic therapy, his condition did not improve and transbronchial biopsies disclosed a typical feature of bronchiolitis obliterans organizing pneumonia (BOOP). After initiation of corticosteroid therapy, there were marked clinical and radiographic improvements. This report demonstrates that chlamydial infection may be associated with BOOP.