OUTLINE: This is a multicenter study. Patients are stratified according to risk (standard risk, defined as age 61-75 and WHO performance status 0-1 vs poor risk, defined as over 75 years and WHO performance status 0-2 OR under 76 years and WHO performance status 2). Frontline therapy: Patients receive gemtuzumab ozogamicin IV over 2 hours on days 1 and 15. Stratum I (Standard risk patients): Patients with disease progression at any time during frontline therapy may begin induction therapy immediately. Induction therapy begins 7-10 days after response assessment regardless of response and in the absence of unacceptable toxicity. Stratum II (Poor risk patients): Patients experiencing complete remission with or without platelet recovery will begin consolidation therapy within 4-8 weeks of response assessment in the absence of unacceptable toxicity. Stratum I Induction therapy: Patients receive mitoxantrone IV over 30 minutes on days 1, 3 and 5; etoposide IV over 1 hour on days 1-3; and cytarabine IV continuously on days 1-7. Patients experiencing partial response are given a second induction therapy course. Patients experiencing complete remission with or without platelet recovery after 1 or 2 induction courses begin consolidation therapy within 4-8 weeks of response assessment in the absence of unacceptable toxicity. Consolidation therapy: Patients receive idarubicin IV on days 1, 3 and 5; etoposide IV over 1 hour on days 1-3; and cytarabine IV continuously on days 1-5. Stratum II Consolidation therapy: Patients receive gemtuzumab ozogamicin IV over 2 hours on day 1 and then 1-3 months later. Patients are followed monthly for 1 year, every 3 months for 2 years, and then every 6 months thereafter.