The Borna disease virus is the cause of cerebral meningitis and encephalitis in sheep and horses. This fatal disease is endemic in the Central Europe region. The virus is characterized by a strong neurotropism and in this respect indicates a considerable affinity to the limbic system. Clinical symptoms of the infection as well as intensity of inflammatory reaction of the c.n.s. "depend on the response on the infected organism's immunological system. In recent years a hypothesis has been posed concerning a probable contribution of this factor to the pathogenesis of some mental and neurological disorders in man. A review of the state-of-the-art research literature on prevalence of infection with the Borna disease virus in affective disorders, schizophrenia, and in some neurological conditions is presented in the paper.