The authors retrospectively reviewed computed tomographic (CT) scans of 18 patients who developed 21 episodes of intrathoracic complications after allogeneic bone marrow transplantation (BMT). Pathologic and/or microbiologic diagnoses were available for all patients. All patients were immunocompromised due to either graft-versus-host disease (GVHD), neutropenia, or recurrent malignancy after BMT. CT demonstrated diagnostically relevant findings that were not apparent at radiography in 12 of the 21 cases (57%). These included a ground-glass pattern in early pneumonia (n = 5); a peripheral distribution in GVHD, bronchiolitis obliterans organizing pneumonia, and eosinophilic drug reaction (n = 4); cavitating lesions in Pneumocystis carinii pneumonia (n = 1); hemorrhagic infarcts in aspergillosis (n = 1); and mediastinal adenopathy in recurrent Hodgkin disease (n = 1). The authors conclude that chest CT is superior to radiography in demonstrating the presence, distribution, and extent of intrathoracic complications developing in patients after allogeneic BMT. CT is useful in guiding procedures for tissue diagnosis.