A 41-year-old man with untreated acute promyelocytic leukemia (APL) was treated with all-trans retinoic acid (ATRA) 80mg/body/day per os. Complete remission was reached in 16 day without bone marrow hypoplasia and aggravated disseminated intravascular coagulation. The chromosomal abnormality, t (15;17), which presented before therapy has not been found since the 29th day of therapy. During the course of induction therapy with ATRA, there was no complication worth of mentioning. Induction therapy with ATRA is thought to be more effective and safer than conventional chemotherapy to attain complete remission in APL. The complete remission has been maintained for 11 months with conventional postremission chemotherapy.