Shortly before the all-trans retinoic acid (ATRA) era, the GIMEMA cooperative group initiated a randomized study comparing idarubicin (IDA) alone with IDA plus arabinosylcytosine (Ara-C) as induction treatment in patients with newly diagnosed hypergranular acute promyelocytic leukemia (APL). Of the 257 patients evaluable for induction treatment, 131 were randomized to receive IDA alone (arm A) and 126 to receive IDA + Ara-C (arm B). Treatment in arm A consisted of 10 mg/m(2) IDA daily for 6 consecutive days, whereas in arm B it consisted of 12 mg/m(2) IDA daily for 4 days combined with 200 mg/m(2) Ara-C daily in continuous infusion for 7 days. Once in complete remission (CR), patients received 3 consolidation courses of standard chemotherapy, and those still in CR at the end of the consolidation were randomized to receive or not receive 1 mg/kg 6-mercaptopurine daily and intramuscular injections of 0.25 mg/kg methotrexate weekly for 2 years. Overall, 100 (76.3%) patients in arm A and 84 (66.6%) patients in arm B achieved CR (P = NS). Event-free survival (EFS) rates were 35% and 23% for patients in arm A and arm B, respectively (P =.0352). Multivariate analysis revealed that EFS was favorably influenced by induction treatment with IDA alone (P =.0352) and unfavorably influenced by white blood cell (WBC) counts greater than 3000/microL (P =.0001) and increasing age (P =.0251). These results indicate that anthracycline monochemotherapy with IDA favorably influences the EFS of patients with newly diagnosed hypergranular APL.