The monograph is devoted to the problem of genetics of mental diseases. The book consists of two parts. The first part includes 6 chapters. It reflects the current state of the problem of oligophrenia, dementia genetics, provides clinical, genetic, biochemical, cytogenetic aspects of individual differentiated forms of oligophrenia and some aspects of medical genetic counseling for families burdened with mental retardation. The second part is devoted to the genetics of schizophrenia, manic-depressive psychosis and epilepsy. Based on a critical analysis of the data accumulated in the world literature, some new provisions and approaches to the study of the genetics of psychosis and convulsive readiness are put forward.