Background:HCV and HBV infection may release autoimmune reactions(AIR).Aim of the study was an assessment of the clinical courseof AIR among HCV and HBV infected patients and the revision of the applied treatment. Material/Methods:22 patients,16 HCV and 6 HBV infected were admitted to the hospital because of symptoms of viral hepatitis and autoimmune hepatitis AIH.Diagnosis of AIH was based on biochemical examinations,presence of autoantibodies and morphological changes in liver biopsy. HCV infection was confirmed by the presence of HCVRNA and HBV infection on the basis of serological markers. Results:The time to develop AIR in HCV infection remained unknown.In HBV infection it took 5 –18 years from the first detection of HBsAg to AIR diagnosis.HBeAg was negative in 5/6 cases of HBV infection.In all HCV cases,HCVRNA was positive.In the group of 22 HCV and HBV patients the titres of autoantibodies were high. The 6/16 HCV and 3/6 HBV patients suffered from extrahepatic localisation of the autoim- mune disease. Chronic hepatitis was confirmed by histological examinations of liver specimens in all patients. The morphological signs of AIH were demonstrated in 6 /16 HCV and 5/6 HBV cases.10/16 HCV and 3/6 HBV were treated with glycocorticoids,3/16 HCV and 2/6 HBV with glycocorticoids and azathioprine. Only 4/16 HCV patients received interferon alpha and 1 out of 6 HBV patients treated with lamivudine.The therapy was ineffective in most of the studied cases. Conclusions: AIR caused many difficulties in the diagnosis and therapy of liver diseases.