Active chronic hepatitis may be associated with various immunologic diseases. In the Mediterranean area and to a lesser extent elsewhere, hepatitis C virus, has often been detected in patients affected by mixed cryoglobulinemia, membranoproliferative glomerulonephritis, polyarteritis nodosa autoimmune type 2b hepatitis, Hashimoto's disease, Sjögren's syndrome and lichen ruber planus. These findings should not be considered fortuitous due to the elevated prevalence of autoantibodies and immunologic abnormalities observed in hepatitis C patients compared with subjects presenting other liver diseases. The pathogenetic evaluation of the association between these immunologic diseases and chronic hepatitis C has led us to suggest that diverse virus C and host induced factors may play a fundamental role in determining these immunologic diseases.