Background: Type II diabetes mellitus (DM) has been shown as more common in patients with hepatitis C virus infection (HCV). Similar data from India is not available. Methods: This 3-year prospective study included consecutive Indian patients with HCV to detect the DM. In all patients, the presence of DM, duration of DM, probable duration of HCV, genotype of HCV, presence of steatosis and presence of cirrhosis were noted. Comparable numbers of consecutive patients with hepatitis B virus infection (HBV) and irritable bowel syndrome (IBS) were analysed for the presence of DM. Results: A total of 200 patients with HCV were analysed: mean age=45.9±9.8 years; male:female=1.3:1; genotype distribution (in 80 patients which included 17 patients of DM)- genotype 3 in 47(58%), genotype 1 in 31(39%) and genotype 2 in 2(3%) patients; probable duration (unknown in 40 patients) of HCV=12.8±8.2 years; steatosis in 55(27.5%) patients; cirrhosis in 88(44%) patients. Of these 200 patients, DM was present in 44(22%) patients with mean duration of DM of 6.1±2.3 years. HCV preceded DM in 29 patients by 10.8±2.3 years. Among HCV with genotype 3, DM was present in 11(23.4%) patients and with genotype 1, DM was present in 6(19.3%) patients. In patients with DM, cirrhosis and steatosis were present in 28(63.6%) and 20(45.4%) patients, respectively, as compared to 60(38.4%) and 35(22.4%) patients without DM. There was significantly lower presence of DM, 24(12%) and 19(9.5%), in 200 patients of HBV and 200 patients of IBS, respectively. Conclusion: There is increased prevalence of DM in patients with HCV. HCV precedes the development of DM by a decade.