SummaryIn order to estimate the prevalence of thalassaemias carriers in the Mediterranean immigrants living in the Brussels region (mainly North Africans), the following determinations have been performed in a group of children attending a general pediatric consultation and in a group of women presenting in a prenatal consultation: blood counts, and measu rements of haemoglobin A2, of serum iron, TIBC and ferritin levels.Among the children studied, 20 % disclosed an iron deficiency, 4,8 % a heterozygote 5 thalassaemia, and 0,4% a probable heterozygote a thalassaemia. Among the women these estimations were respectively 8.1, 2.6 and 0%.The authors estimate that the birth of one homozygote children may be awaited each year in the Brussels region. The annual cost of his treatment is higher than that of a prospective prevention which would be based on determination of the level of haemoglobin A2in all immigrate parturients disclosing microcytosis.