The main clinical and haematological features of sickle cell patients were compared in 618 French, 50 Guianese and 87 Algerian patients. In homozygous sickle cell patients, the proportion of icteric subjects rises with age in all centres; the prevalence of splenomegaly reaches a peak in children from 1 to 5 years and then decreases; jaundice and splenomegaly are more often noted in Algerian and Guianese than French patients. The prevalence of painful crisis is comparable in the 3 centres. In 465 French SS children, having a mean age of 7.3 +/- 5.9 years, the prevalence of a past history of meningitis is 7.3%, of septicaemia 4.1% of osteomyelitis 8.8%. These percentages do not differ significantly between countries. Prevalence of a past history of cerebrovascular accident is 3.2% in French SS patients; 1.2% in SC, 3.8% in S beta thalassaemia. A past history of acute splenic sequestration was noted significantly more often in SS (11.75%) and S beta thalassaemia (14.3%) than SC (3.6%) in French children (p < 0.05). Proportions of subjects transfused at least once do not differ between countries; SS children are more transfused (64%) than SC (15.6%) and S beta thalassaemic (66%) (p < 10-4). Haemoglobin and reticulocyte counts do not differ significantly between countries. In conclusion, no major differences were detected between French, Guianese and Algerian homozygous sickle cell patients: this may be due to the fact that France is in itself a mosaïc of ethnic origins.