Severe respiratory distress appeared in a 14-year-old girl with acute lymphoblastic leukemia 2 months after receiving syngeneic bone marrow transplantation (BMT) with a conditioning regimen of a high-dose of busulfan, etoposide and nimustine. Rapid body-weight gain and edema, especially in eyelids and lower-limbs, were also observed. Without any findings of heart failure nor GVHD, pulmonary edema was recognized on the chest roentgenogram. As soon as the diagnosis of pulmonary edema due to 'capillary leak syndrome' was suspected, the patient was treated with intravenous administration of diuretics, albumin and bolus methylprednisolone in combination of mechanical ventilation. Although the clinical manifestations were improved by the treatment, the disease recurred 5 weeks later. The patient was successfully treated by the same medications, and there has been no recurrence as of the sixth month after discontinuance of the therapy. At present, the mechanism of capillary leak syndrome is still undefined. In this case, however, we speculate that the conditioning regimen for BMT intensified the capillary disturbance initially caused by intensive chemotherapy since remission induction. Furthermore hypoalbuminemia due to severe anorexia might have enhanced the occurrence of the disease.