One hundred twelve patients with geriatric acute myeloid leukemia (AML), refractory or relapsed AML, or myelodysplastic syndrome and refractory anemia with excess of blasts in transformation (MDS-RAEBt) were entered into this study to receive CAG (aclarubicin and low-dose cytosine arabinoside [Ara-C]in combination with granulocyte colony-stimulating factor [G-CSF]) with the objective of evaluating the efficacy and tolerance of this regimen. Low-dose Ara-C was given subcutaneously at a dosage of 10 mg/m2 every 12 hours on days 1 to 14. Aclarubicin was administered intravenously at a dosage of 14 mg/m2 per day on days 1 to 4 (CAG regimen A) or 7 mg/m2 on days 1 to 8 (CAG regimen B). Recombinant G-CSF was given subcutaneously at a dosage of 200 3g/m2 per day on days 1 to 14. We demonstrated comparable overall complete remission rates for the 4 groups of patients: 30.8% (8/26) in the elderly patients, 48.4% (30/62) in the refractory AML patients, 44.4% (8/18) in the relapsed AML patients, and 38.5% (5/13) in the MDS-RAEBt patients. Of the 52 patients followed up, the 12-month progression-free survival (PFS) and overall survival (OS) rates estimated by the Kaplan-Meier method were 40.73% 3 8.15% and 42.85% 3 8.23%, respectively. The median PFS and OS times were 9.0 3 2.2 months and 11.0 3 1.6 months, respectively. Toxic effects were very rare and mainly consisted of neutropenia and thrombocytopenia due to myelosuppression; approximately 70% to 80% of patients had neutropenia or thrombocytopenia that exceeded National Cancer Institute grade II. Nonhematologic toxicities were not observed in this study. The CAG regimen seems promising, with acceptable toxicity, for the treatment of various categories of poor-prognosis AML and MDS-RAEBt.