The aim of this study was to investigate whether or not the diabetes mellitus may be considered a risk factor for the HCV infection. The HCV seroprevalence was evaluated in 254 diabetic subjects, whose anamnestic data and risk factors are known, in comparison to 223 first-time blood donors, carefully age- and gender-matched. The statistical analysis showed that the studied groups belonged to the same population (Mann-Whitney U test) and that there were no significant differences between cases and controls as regards HCV prevalence (Yates corrected chi 2 test). The obtained data underline the importance of the control group selection, especially in the studies considering age-related pathologies. The authors disprove type 2 diabetes as a risk factor for the HCV infection and consider that this is a valid hypothesis only when the hepatitis C was unknown and not adequate prevention was used.