A 22-year-old man with T cell type acute lymphoblastic leukemia in first remission underwent autologous bone marrow transplantation (BMT). The preparative regimen included cytosine arabinoside, cyclophosphamide and fractionated total body irradiation. His harvested bone marrow cells were purged with 4-hydroperoxycyclophosphamide. His serological test was positive for cytomegalovirus (CMV) before the BMT. On day 53 after the BMT, he developed dry cough and his chest X-ray film showed bilateral basilar infiltration. Bronchoalveolar lavage was performed and cytology of the specimen revealed typical cytomegaloviral inclusion bodies. DNA analysis and viral culture of the specimen were also positive for CMV. The patient was started on ganciclovir and immunoglobulin with high dose methylprednisolone. His respiratory status deteriorated, however, and the patient expired because of respiratory failure. Autopsy revealed severe interstitial pneumonitis with suppression of CMV replication from the treatment. Interstitial pneumonitis due to CMV should be considered as a significant complication of autologous BMT.