Follow-up of the over-35 cohort is important because it was not so long ago that it was estimated that 50 percent of patients with sickle cell anemia in the United States died before their twentieth birthday. However, data accumulated over the past eight years by the CSSCD demonstrates that this is incorrect. Survival beyond the age of forty suggests that surviving patients are somehow different from other patients with a high mortality in the earlier years. Therefore, they constitute a cohort of special interest, and the reasons for prolonged survival in this disease remain to be well documented prospectively. Technology is now available to identify genetic differences which may influence survival.