Comprehensive evaluations of the clinical status of patients were usually carried out only during hospitalizations for 'crises' or other acute illnesses. Because of this inconsistent nature of the doctor/patient relationships, methods of periodic recording of the patient's status needed to be established. Further, the obtaining of comprehensive laboratory data was necessary during periods of apparent clinical remissions as well as hospitalizations. A well designed, statistically valid, longitudinal study could make a significant contribution to a better understanding of sickle cell disease. Information was particularly lacking on the clinical course starting at birth. Criteria needed to be formulated that could establish classifications of organ involvement and severity of the disease processes. Such classifications could ultimately be used in establishing the need for and evaluating the efficacy of proposed therapies.