Systemic rheumatological diseases are often accompanied by the development of central and peripheral nervous system pathology. Data providing evidence of the high incidence of peripheral nervous system lesions in systemic lupus erythematosus and systemic scleroderma are presented. These diseases in particular are characterized by polyneuropathies and tunnel syndromes. Our own observations, along with published data, revealed the following major pathogenetic mechanisms of peripheral nervous system lesions in diffuse connective tissue diseases - ischemic, immunological, and metabolic. Consideration of these mechanisms will lead to pathogenetically based treatment and improved therapeutic outcomes.