All-trans-retinoic acid is an effective agent to induce remission in patients with acute promyelocytic leukemia (APL). Unlike conventional chemotherapy, this drug exerts its effect by inducing differentiation of immature leukemic cells. A distinctive clinical syndrome characterized by fever, dyspnea, effusions, weight gain, and organ failure (the "retinoic acid syndrome") can occur during treatment with this drug. Postmortem studies have shown extensive organ infiltration by leukemic cells, and the early administration of corticosteroids can result in prompt resolution of symptoms. We describe a patient with APL in whom acute renal failure developed during treatment with all-trans-retinoic acid. Transient renal enlargement during a period of leukocytosis and a beneficial response to treatment with dexamethasone suggest that renal failure in this patient was probably related to the retinoic acid syndrome.