Marriages between close blood relatives are discouraged or even illegal in many Western countries. On contrast in many countries there is a strong cultural preference for consanguineous marriages, which is most commonly contracted between first cousins. Consanguinity and its impact in clinical genetics have been appreciated with interest by both clinical geneticists and social scientists for many years. Misconceptions about basic genetic concepts and inheritance pattern are widespread not only among the general population but also among the health care providers. The purpose of this article is to provide a concise summary of the basic concept of consanguinity and its implication in clinical genetics.