A 46-year-old woman with acute promyelocytic leukemia (APL) was treated with all-trans retinoic acid (ATRA) and chemotherapy according to the AML-92, M3 regimen of the Japan Adult Leukemia Study Group (JALSG). Between days 7 and 18 of therapy, she suffered chest discomfort, fever, cough, dyspnea and general fatigue. A chest roentogenogram showed bilateral interstitial infiltrates. Her leukocyte count began to increase rapidly to 6,400/microliters on day 14. Marked hypoxia (PO2 35.9 mmHg) suggested occurrence of retinoic acid (RA) syndrome. She underwent endotracheal intubation and mechanical ventilation with administration of methyl-prednisolone (m-PSL) pulse therapy. Her symptoms promptly abated. Therapy with ATRA was continued and her leukocyte count reached 44,800/microliters on day 19 of therapy. She achieved complete remission on day 48.