Aim. To estimate the spread of insulin resistance (IR) in patients with chronic hepatitis C (CHC) and to define the role of IR in the development of hepatic steatosis (HS) and in the progression of liver fibrosis (LF), as well as the impact of IR on the results of antiviral therapy (AVT). Subjects and methods. A total of 211 patients with CHC were examined. A comparison group consisted of 75 patients with chronic hepatitis B (CHB). The patients were divided according to the presence and absence of IR and type 2 diabetes mellitus (DM). IR was analyzed in patients with CHC with a body mass index (BMI) of <25 kg/m2 and with the initial manifestations of LF. Results. In the patients with CHC, IR without DM was 1.7-fold more common and type 2 DM was 2.6 times more frequently seen than in those with CHB. The highest biochemical activity, subclinical inflammation (as evaluated from ferritin and C-reactive protein levels), and an advanced LF stage were noted in the presence of IR and type DM. IR and type 2 DM were associated with metabolic syndrome and its individual components and with no response to AVT. When the BMI was <25 kg/m2, HS, inadequate 25(OH)D provision, an advanced LF stage, and slowly progressive inflammation were related to IR. In the presence of the initial manifestations of fibrosis, IR was associated with obesity, HS, 25(OH)D deficiency, a rise in C-reactive protein greater than 3 mg/l, and no response to AVT. Conclusion. The presence of IR in CHC patients with a BMI of <25 kg/m2 and with the initial manifestations of LF and the association of IR with HS and an advanced LF stage necessitate an examination of all patients with CHC in an effort to identify IR and to perform active therapy of detected abnormalities.