Recent clinical and experimental data indicate that statins have effects beyond cholesterol lowering that may be beneficial in sickle cell disease by protecting the vascular endothelium. Statins have been shown to attenuate endothelial dysfunction through their anti-inflammatory, anti-oxidant and anti-thrombotic properties. This phase I/II dose-escalating trial is designed to assess the safety and potential clinical efficacy of oral simvastatin (Zocor)in adolescents and adults with sickle cell disease (SCD).