Fatal neutropenic enterocolitis was seen in a patient undergoing autologous bone marrow transplantation for non-Hodgkin's lymphoma. Excessive drug action due to a mildly diminished creatinine clearance could have contributed to the pathogenesis. Computed tomographic scanning and ultrasonography demonstrated pneumatosis of the gastrointestinal tract, but the disease had become extensive by then. Necrotizing enterocolitis should be suspected early in a granulocytopenic patient with abdominal pain and diarrhea or vomiting. Aggressive surgical or medical management may avoid a fatal outcome.