This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Hydroxyurea (HU) has demonstrated laboratory and clinical efficacy for adults with sickle cell anemia (SCA). Pediatric patients with SCA also benefit from HU therapy. Although HU therapy has emerged as an exciting and efficacious therapeutic agent for patients with SCA, important issues remain regarding its use, especially for those less than 2 years old. The primary objective of this study is to determine whether daily oral hydroxyurea can reduce by [unreadable]50% chronic organ damage that develops in young children with SCA. Secondary objectives of this study include: 1) to determine the relationship between fetal hemoglobin levels and chronic organ damage in young children with SCA and 2) investigate the safety of HU for young children with SCA regarding a) physical growth and development, b) neuropsychological development, c) immunological responses, and d) mutagenic effects on DNA.