Spontaneous pneumothorax following unrelated hematopoietic stem cell transplantation developed in our 2 patients with bronchiolitis obliterans. Bronchiolitis obliterans is a form of obstructive airway disease and is considered a manifestation of chronic graft-versus-host disease (GVHD). Both of the patients were the recipients of marrow from HLA-matched unrelated donors after a preparative regimen with total body irradiation. Chronic GVHD after transplantation is a common feature in these cases. In contrast to other patients with pneumothorax described in the literature, our patients did not develop bullae. We describe a pneumothorax secondary to bronchiolitis obliterans that complicated the posttransplantation course.