Stroke is a serious problem for children with sickle cell anemia.  Even with prompt recognition and emergency medical management, the effects of stroke in children with sickle cell anemia are significant and many affected children have substantial residual motor and cognitive deficits. Children with sickle cell anemia who have high measurements of Transcranial Doppler (TCD), which measures blood flow of the brain, are at high risk to have a stroke. Children with high measurements of TCD receive monthly blood transfusions to help reduce the risk of stroke. However, there are various problems associated with transfusions, such as, not getting full protection against stroke, risk of infection, cost, shorter life, and iron overload.

The purpose of this study is to see if using an alternative treatment by the use of hydroxyurea medication can help reduce the risk of stroke by lowering TCD levels in a similar way as monthly blood transfusions do. This study will also compare the standard treatment (blood transfusions) with the alternative treatment (hydroxyurea) for effects on growth and development, the frequency of brain-related stroke and non-stroke events, other sickle-related events, and quality of life.