This paper reviews the most important aspects of carrier detection procedures, genetic counselling, population screening and prenatal diagnosis of the thalassaemias and sickle cell anaemia. Carrier detection can be made retrospectively, following the birth of an affected child, or prospectively. Carrier detection and genetic counselling in at-risk populations for alpha-thalassaemia and sickle cell anaemia is carried out mostly retrospectively. However prospective carrier screening is ongoing in Cuba and Guadeloupe for sickle cell anaemia and, in a very limited way, in some South East Asian populations, for alpha-thalassaemia. For beta-thalassaemia, several programmes, based on carrier screening and counselling of couples at marriage, preconception or early pregnancy, are operating in several Mediterranean at-risk populations. These programmes have been very effective, as indicated by increasing knowledge on thalassaemia and its prevention by the target population and by the marked decline of the incidence of thalassaemia major. Carrier detection is carried out by haematological methods followed by mutation detection by DNA analysis. Prenatal diagnosis is accomplished by mutation analysis on PCR-amplified DNA from chorionic villi. Future prospects include automation of the process of mutation-detection, simplification of preconception and preimplantation diagnosis and fetal diagnosis by analysis of fetal cells in maternal circulation.