We report on a patient with chronic myelogenous leukemia who developed bronchiolitis obliterans organizing pneumonia (BOOP) after allogeneic bone marrow transplantation (BMT). A 19-year-old Japanese male complained of dry cough and dyspnea 7 months after BMT. The chest X-ray and computed tomography revealed patchy infiltrates bilaterally. Lung function test, lung biopsy and bronchoalveolar lavage were consistent with the diagnosis of BOOP. The patient also suffered from suspected graft-versus-host disease (GVHD) of the liver, after discontinuation of cyclosporine. Furthermore, prednisolone proved effective against the BOOP and the liver dysfunction. These findings indicate that BOOP is a possible pulmonary manifestation of chronic GVHD, and that immunological mechanisms may have effected the onset of BOOP after BMT in this case.