In patients with hereditary haematologic diseases risk of repetition of these anomalies in brothers and sisters of probands and their progenies was assessed. In haemiphilia and Wiskott-Aldrich's. thrombocytopenia, both caused by a mutant gene in an X chromosome, prenatal pole determination was consulted in order to have a pregnancy with a male fetus interrupted due to high risk. Dominantly hereditary spherocytosis, eliptocytosis, chronic benign neutropenia are the diseases which do not appear in such a severe form that ceasation of further pregnancies should be consulted, instead, an early postnatal diagnosis is suggested to the families with increased risk of these anomalies. In the recessive hereditary beta thalassemia and in Fanconi's anemia in which prenatal diagnosis can not be made for the time being, level of risk for the further children is told to the parents after the child has been born. The parents are then left to decide whether to take a risk and have other children who might suffer of these severe haemolitic diseases. In the haemolitic diseases with often occurrence in certain families, but in which the manner of inheritance is not clear, as for example in the Kasebach-Meritt's syndrome, risk for the following children is uncertainly increased so that the genetic counsel is uncertain and unprecise. In the hereditary haemolitic diseases which appear sporadically, either of known or unknown etiology, such as congenital teleangiectasis of capillary vessels or Sturge-Weber's syndrome with severe vascular and nerval disorders, the parents are stimulated to further pregnancies as they are not followed by increased risk.