Idarubicin is a new derivative of Daunorubicin which was found to be more potent and more active than Daunorubicin and Doxorubicin in several experimental leukemias. Its antileukemic activity in preclinical models prompted the introduction of Idarubicin into clinical studies. As a single agent, Idarubicin produced complete remission in 20% and 30% of patients with heavily pretreated pediatric and adult acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) respectively. Idarubicin combined with Cytarabine and/or other antileukemic agents produced complete remissions in 46% of patients with refractory or relapsed AML and in 58% of patients with refractory or relapsed ALL (adult and pediatric). Subsequently, Idarubicin has been employed in untreated AML patients in combination with Cytarabine and/or Etoposide, producing complete remissions in more than 80% of patients. In ALL patients the drug has been used in combination with Vincristine, Cytarabine and Prednisone, producing complete remissions in 82% of patients. Recently, Idarubicin has been utilized in combination with intermediate doses of Cytarabine in refractory or relapsed ALL and AML, and 70% of patients achieved complete remission. Preliminary results of ongoing prospective randomized studies in untreated adult AML seem indicate that Idarubicin is at least equivalent, if not superior to Daunorubicin. The antileukemic activity of Idarubicin given orally as single agent, or in combination with other drugs, has been shown in AML and myelodysplastic syndromes. The toxicity of Idarubicin includes mild nausea and vomiting, alopecia and liver dysfunction. Ongoing randomized trials comparing Idarubicin to Daunorubicin should provide more information about the potential cardiotoxicity of this drug.