The clinical, haematological and biochemical features of 50 Sudanese patients with sickle cell disease (SCD) were determined. Of 23 patients with complete family data, 21 had sickle cell anaemia (homozygous HbSS), 2 had sickle-cell/beta+thalassaemia but none had sickle cell/beta Othalassaemia. The remaining 27 patients had HbSS phenotype. 84% of patients were from the Baggara tribe in western Sudan, where HbS is a natural extension of the west African HbS belt. 21 patients were children under 2 years old; 19 were 3-10 years old; and the remaining 10 were over 10 years old. Young patients presented mainly with painful vaso-occlusive crisis, severe anaemia, hand and foot syndrome, fever, underweight, malnutrition and various infectious diseases. All patients had mild to moderate cardiac enlargment; 42% had a moderately enlarged spleen but only 10% had an enlarged liver; 20% had infarctive lesions of long bones and another 8% had Salmonella osteomyelitis. Leg ulcers, priapism, enuresis and cholelithiasis were not observed. Patients had a mean haemoglobin concentration of 7.3 g/dl; reticulocyte count of 15.1%; serum bilirubin of 2.1 mg/dl; HbA2 level of 2.8% and HbF of 7%. Thus, the observed pattern of SCD in Sudan is comparable to the severe type described for Africans and not comparable to the benign form found in Shiite Moslem Arabs of Saudi Arabia. 6 adults with mild SCD had HbF levels below 5%. Amelioration of the disease, therefore, does not seem to be related to HbF levels; nor was it possible to relate it to high levels of erythrocyte 2,3-diphosphoglycerate.