Pulmonary complications are a common cause of morbidity and mortality after bone marrow transplantation. Some of these complications are infectious and related to the degree of ongoing immunosuppression, and thus vary with the posttransplant marrow reconstitution and the need for continued immunomodulating drugs. Noninfectious complications are related to previous chemotherapy, the transplantation protocol and conditioning regimen, and, in allogeneic transplants, the presence of graft-versus-host disease. The various complications are classified based on their timing after the transplant procedure. A diagnostic and therapeutic approach is outlined and the prognosis is discussed.