The role of genetic factors in the etiology and pathogenesis of various human diseases is discussed. General characteristics and features of inheritance of chromosomal, monogenic and multifactorial diseases are presented. Clinical and molecular genetic description of more than 370 inherited diseases classified according to the system principle is given. Particular attention is paid to clinical polymorphism and genetic heterogeneity of hereditary pathologies. 3 final chapters are devoted to the prevention, pharmacogenetics and treatment possibilities of hereditary diseases.