Beginning in 1996, a five year follow-up of the adult patients in MSH was initiated. The purpose was to ascertain the long-term effects of hydroxyurea in this patient population. Patients were followed annually to determine health status, quality of life, incidence of malignancies, and birth defects in their offspring. In addition, mortality rates were determined so that a comparison could be made between this cohort and the mortality data from the Cooperative Study of Sickle Cell Disease (CSSCD) adult cohort and the normal African-American population mortality data. The follow-up was conducted in three phases. Phase I or the Planning Phase in which the final protocol was developed, lasted three months. Phase II, patient entry between March 1996 and June 1996 and patient follow-up, extended from the fourth to the 48th month. Phase III, patient exit and data analysis, were carried out during the final nine months of the study.