The features of 4 allogeneic bone marrow transplant patients with an unusual late-onset complication of pulmonary abnormalities with small chronic pneumothoraces are described. Thin-section computed tomography demonstrated upper zone fibrotic changes and diffuse abnormalities suggestive of constrictive obliterative bronchiolitis. An important feature of the pneumothoraces was that they tended to be recurrent and small. We suggest that awareness of this unusual association may be useful in the radiologic evaluation of late-onset pulmonary complications after allogeneic bone marrow transplantation.