A total of 422 patients with sickle cell disorders have been observed for 3,442 patient years. During this period, 53 episodes of septicemia or meningitis occurred, indicating a risk of 12.5% from these infections for each individual. If only patients with SS hemoglobinopathy (sickle cell anemia) (323 patients) are considered, the risk was 15.2%. The case fatality ratios for sepsis and meningitis were 35% and 10%, respectively. Disease due to Streptococcus pneumoniae occurred, almost exclusively, among children with SS hemoglobinopathy who were less than 5 years of age. After the first decade, illnesses among patients with all types of sickle cell disorders were frequently associated with an identifiable source of infection, a chronic course, and frequent involvement of Gram-negative organisms.