A study of the natural history of sickle hemoglobinopathies was begun in March 1979. By August 1987, a total of 2824 patients less than 20 years of age were enrolled. There have been 14,670 person-years of follow-up. Seventy-three deaths have occurred. Most of the deaths were in patients with hemoglobin SS. The peak incidence of death was between 1 and 3 years of age, and the major cause in these young patients was infection. Cerebrovascular accidents and traumatic events exceeded infections as a cause of death in patients greater than 10 years of age. There was limited success in identifying risk factors for death. Comparison of this study's overall mortality of 2.6% (0.5 deaths per 100 person-years) with previous reports indicates improvement of survival in US patients less than 20 years of age with sickle hemoglobinopathies. This improvement is most likely due to parental education and counseling about the illness and the early institution of antibiotics in suspected infections.