Hepatitis C virus (HCV) infects mononuclear cells and may be responsible, as are other viruses, for immunologic disorders. The immunologic abnormalities observed in HCV infections are usually non-specific (i.e. cryoglobulinemia, immune complex deposits, autoantibodies). The association with cryoglobulinemia is clear and cryoglobulinemia-related symptoms are usually improved by interferon alpha treatment, although patients often relapse after the end of treatment. The relationship with other immunologic abnormalities is less clear. The occurrence of antismooth muscle or anti-nuclear antibodies does not seem significantly different in hepatitis C infection than in other hepatic disorders, particularly hepatitis B. However, anti-liver kidney microsomal (LKM1) antibodies are present significantly more often than in patients with other liver diseases. When clinical, histologic and biological findings suggest HCV infection with chronic hepatitis, interferon alpha or combination therapy with ribavirin are treatment options When the clinical context and results of laboratory tests suggest an autoimmune disorder or overlap syndromes (i.e. both autoimmune and viral hepatitis), interferon should not be given as a first intention, since revelation or exacerbation of autoimmune hepatitis has been reported with interferon. A marked prevalence of anti-HCV antibodies has also been reported in patients with sialadenitis, lichen planus and thyroiditis. Interferon may induce or worsen these immunologic diseases, but there are very few studies showing improvement of these manifestations with interferon.