In 1995, the Multicenter Study of Hydroxyurea (MSH) demonstrated that hydroxyurea is effective in decreasing the frequency of painful crises, hospitalizations for crises, acute chest syndrome, and blood transfusions by 50%. The recently completed phase II study of hydroxyurea in children (PED HUG) demonstrated that children have a response to hydroxyurea similar to that seen in adults in terms of increasing fetal hemoglobin levels and total hemoglobin, and decreasing complications associated with sickle cell anemia. In addition, this study demonstrated that the drug does not adversely affect growth and development between the ages of 5 and 15. A recently completed pilot study of hydroxyurea given to children between the ages of 6 months and 24 months demonstrated that the drug is tolerated well by small infant, and that the fetal hemoglobin switch can be forced to remain in the "on position" by hydroxyurea administration.