Pulmonary interstitial infiltrates developed in a 22-year-old female after bone marrow transplantation (BMT) for acute lymphoblastic leukemia (ALL) in second remission. She was receiving prednisone for graft versus host disease (GvH). There was some evidence of cardiac failure, but the primary diagnosis was that of cytomegalovirus (CMV) pneumonia, which resolved. Recurrent infiltrates were associated with the appearance of fat emboli in the pulmonary capillaries. There was little histological evidence of CMV pneumonitis, although other tests confirmed persistent infection. The patient recovered after further treatment directed at CMV infection and cardiac failure with a modest reduction in steroid dose. Most previous descriptions of pulmonary fat embolization (PFE) in immunocompromised patients have been derived from autopsy studies, and the majority of patients have received steroid therapy. The present case illustrates that PFE may complicate or contribute to the picture of interstitial pneumonitis (IPN) in the BMT recipient and that this syndrome may be reversible.