The authors give a summing up of ten years of genetic counselling concerning 1271 requests and single out two equally important categories of consultants. The first might require premarital counselling (in cases of consanguineous unions, or when one of the partners or relatives are affected) but, in fact, come to consultation, four times out of ten, after marriage and even after procreation. The consultants of the second group need prenatal counselling either because a child suffers from a hereditary disorder, or because earlier pregnancies did not come to term. Whichever the type, one consultation out of seven concerned a pregnant woman. A classification by type disorder and by mode of transmission is given.