Patients receive idarubicin IV over 15 minutes on days 1-3, cladribine IV over 2 hours on days 1-5, and filgrastim (G-CSF) subcutaneously beginning on day 6 and continuing until blood counts have recovered for 2 days. Treatment repeats every 3 weeks for up to 2 courses in the absence of disease progression or unacceptable toxicity. Patients who achieve complete response after completion of course 1 may proceed to other chemotherapy or bone marrow transplantation at the discretion of the protocol investigator. Patients with extramedullary disease may receive intrathecal chemotherapy or radiotherapy to symptomatic sites.