Molecular genetic aspects of the inherited bleeding disorders haemophilia A and B, deficiencies of factor VII and X are described. The spectrum of the mutations is characterized. For genetic counselling the X-chromosomal inheritance of haemophilia and the principles of the indirect and direct genomic diagnosis are explained. Clinics and genetics of the rare inherited bleeding disorders known as factor VII and factor X deficiency are summarized. The mutations spectrum, the role of polymorphisms, the bleeding pattern and genotype-phenotype relations are described.