A study of the natural history of sickle hemoglobinopathies was begun in March 1979. By August 1987, a total of 2824 patients <20 years of age were enrolled. There have been 14 670 person-years of followup. 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 > 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 <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 antibotics in suspected infections.