BABY HUG is a randomized, double-blind, placebo-controlled study to determine if hydroxyurea can prevent the onset of chronic end organ damage in young children with sickle cell anemia. Approximately 200 children with sickle cell disease will be recruited to receive either hydroxyurea or placebo. The children will be screened at study entry for signs of abnormal brain, kidney, pulmonary, and splenic function, and developmental milestones. They will then be randomly assigned to receive either hydroxyurea or placebo and followed yearly to assess chronic end organ damage of the major organ systems. The primary endpoint will be a 50% reduction in rates of damage to the major organs with surrogate markers of organ function during follow-up in Phase II of the trial.