Clinical experience with hydroxyurea for patients with sickle cell disease (SCD) has been accumulating for the past 25 years. The bulk of the current evidence suggests that hydroxyurea is well-tolerated, safe, and efficacious for most patients with SCD. Hydroxyurea has proven clinical efficacy for reducing acute vaso-occlusive events including pain episodes and acute chest syndrome. Salutary effects on hematological parameters include increases in fetal hemoglobin (HbF), hemoglobin, and MCV; also significant decreases occur in WBC, ANC, reticulocytes, LDH, and bilirubin. Treatment with hydroxyurea is usually considered for patients with recurrent vaso-occlusive events, but additional indications for treatment may include laboratory markers of disease severity and evidence of chronic organ dysfunction. Ten years ago, the US Food and Drug Administration approved hydroxyurea for adult patients with clinically severe SCD; however, its use in children remains off-label. Despite the large body of evidence regarding its efficacy and safety, hydroxyurea is currently prescribed only sparingly for patients with SCD and therefore has only limited effectiveness for this disorder; barriers to its use need to be identified and overcome.