Differentiation therapy with all-trans retinoic acid (ATRA, tretinoin) alone or in combination with chemotherapy induces around 90% complete remission in acute promyelocytic leukemia (APL). By giving non-cross resistant chemotherapy as postremission therapy, more than 50% of APL, especially more than 70% of APL patients of age less than 30, became curable. Since this active form of Vitamin A causes less toxicity and fewer complications compared with other cytotoxic drugs, the medical costs required are less. Therefore, ATRA therapy should be incorporated as a first-line therapy for APL.