We have previously demonstrated that 5-aza-2′-deoxycytidine (decitabine) augments fetal hemoglobin (HbF) levels in patients with sickle cell anemia (SS) who did not respond to hydroxyurea (HU). The present study was designed to determine the effect of repeated decitabine dosing on HbF levels and hematologic toxicity over a 9-month treatment period. Seven patients (5 HU nonresponders) were entered. One patient had α-thalassemia sickle cell anemia. Decitabine was administered by intravenous infusion at a starting dose of 0.3 mg/kg per day, 5 days a week for 2 weeks, followed by a 4-week observation period. If the absolute neutrophil count dropped below 1000, the dose was reduced by 0.05 mg/kg per day in the next cycle. A drug dose was obtained for each patient, and it resulted in an elevated HbF without neutropenia (absolute neutrophil count nadir greater than 1500) or evidence of cumulative toxicity. Average HbF and average maximal HbF levels attained during the last 20 weeks of treatment for the 6 SS patients increased to 13.93% ± 2.75% and 18.35% ± 4.46%, respectively, from a pretreatment mean of 3.12% ± 2.75%. Mean and mean maximal hemoglobin (Hb) levels increased from 7.23 ± 2.35 g/dL to 8.81 ± 0.42 g/dL and 9.73 ± 0.53 g/dL, respectively. Individual maximal F-cell number observed during the trial was 69% ± 10.12%. The absence of cumulative toxicity may allow shorter intervals between drug treatments, which may lead to higher hemoglobin and HbF levels after several treatment cycles and, therefore, to greater clinical improvement.