In the last fifteen years, therapeutic use of intravenous immunoglobulin on one hand, and of bone marrow transplantation on the other, have largely modified survival rate and prognosis for many primary immunodeficiency diseases. At the same time, major advances in molecular genetics have allowed mapping of several immunodeficiency genes and made prenatal diagnosis feasible. Furthermore, for many X-linked immunodeficiencies, carrier detection can be also accomplished by means of analysis of the pattern of X-chromosome inactivation. As a whole, these techniques have substantially contributed to a more accurate genetic counseling in the families.