Purpose: The objective of this contract is for the Contractor to serve as a clinical center for the Pediatric Hydroxyurea Phase III Clinical Trial (BABY HUG). The clinical trial will include a medical coordinating center, 10 pediatric clinical centers, a pharmacy distribution center, a blood chemistry laboratory, and a cytogenetics laboratory. The trial is a randomized, double blind placebo controlled trial to determine if hydroxyurea therapy is effective in the prevention of chronic end organ damage in pediatric patients with sickle cell anemia (HbSS). The clinical center is responsible for recruitment, enrollment, and patient follow-up examinations for the purpose of monitoring clinical responsiveness to study treatments, to assess growth and development, and to monitor for toxicity to study treatments. The protocol included a Feasibility and Safety pilot beginning at 1 year of age, that recruited 40 children. After the data from the first 40 subjects were reviewed by the DSMB, full recruitment of the remaining sample size began. The IND number was obtained from the Food and Drug Administration (FDA) in April, 2003. NHLBI formed a partnership with NICHD under the Best Pharmaceuticals for Children Act (BPCA) to collaborate on the conduct of BABY HUG. Under the BPCA, if efficacy and safety of hydroxyurea are proven, NICHD will present the BABY HUG data set to the FDA so that the label for hydroxyurea can be changed to include young children with sickle cell anemia. NICHD contributed funds to pay for adding new clinical sites as satellites, study drug manufacturing, and pharmacokinetics analyses.