We examined the incidence and clinical outcome of late-onset noninfectious pulmonary complications (LONIPC) in a series of 234 patients who underwent allogeneic bone marrow transplantation at our institution between April 1982 and October 1996. The 179 patients who survived 3 months or more were evaluated. Clinical, radiologic, pulmonary function, and pathologic tests were reviewed to identify 18 patients (10%) who fulfilled the diagnostic criteria of LONIPC. Accordingly, the pulmonary processes included bronchiolitis obliterans (BO, five patients), bronchiolitis obliterans with organizing pneumonia (BOOP, three patients), diffuse alveolar damage (DAD, one patient), lymphocytic interstitial pneumonia (LIP, one patient), and nonclassifiable interstitial pneumonia (NCIP, eight patients). Various methods of enhanced immunosuppressive therapy resulted in marked durable remission in nine patients (50%) (3/3 with BOOP, 3/8 with NCIP, 1/1 with DAD, 1/1 with LIP, 1/5 with BO). The presence of chronic graft-versus-host disease (cGVHD) and prophylaxis for GVHD with cyclosporine and prednisone were the only variables significantly associated with the development of LONIPC (P = 0.0001 and 0.008, respectively). Regardless of histology, a reduction in the forced expiratory volume to < 45% of the predicted range was associated with poor response to treatment. These findings suggest a strong association between cGVHD and LONIPC and that the risk of LONIPC development may be influenced by the particular method of GVHD prophylaxis. Most patients with BOOP or mild airflow limitation at diagnosis achieved durable remissions.