The article covers the mechanisms of thyroid involvement in viral hepatitis C. Direct damaging effect of the virus on the gland, autoimmune destruction of thyrocytes and their combination are described. We revised case histories of 46 patients with active form of viral hepatitis C (RNA +). According to the results of ultrasound investigation we have detected heterogenous structure of the gland in 10 (21.7 %) patients, and its enlargement to I stage — in 12 (26.0 %) patients. Increased levels of thyroid peroxidase antibodies were observed in 12 (26.1 %) patients. Changes of fT4 and fT3 were not significant. In 4 (10.9 %) female patients we have detected clinically significant increased level of thyroid-stimulating hormone and diagnosed them with hypothyroidism and autoimmune thyroiditis. Female patients were more prone to the appearance of virus-associated thyroid involvement.