Sickle cell anemia (Hb SS) and related hemoglobinopathies involving sickle hemoglobin (HbS) had been recognized for many years and numerous clinical and laboratory manifestations had been described. However, the clinical course of sickle cell disease was poorly documented. The ability to establish concrete interrelationships among signs, symptoms and laboratory test results was complicated by the complexity of the interaction of basic disease processes with other health related events.