This study was carried out to determine the prevalence of hepatitis C virus (HCV) antibodies and the epidemiologic factors associated with HCV infection in patients with chronic renal failure before the onset of ESRD. Sex, age, type of renal disease, level of renal function, and history of blood transfusions and invasive procedures were analyzed in 226 patients with renal disease, compared with a population of 1,244 normal subjects and 124 patients with impaired immunity (patients having autoimmune diseases and receiving chemotherapy treatment). Eighteen seropositive patients with renal disease (prevalence, 7.9%) were found, which was significantly higher than the prevalence in the normal population (1.03% in blood donors, 0.98% in pregnant women; P < 0.001, chi 2). There was no significant association of sex, number of blood transfusions, or history of invasive procedures with the presence of HCV antibodies. The prevalence of HCV antibodies was higher (16.6%) in patients with glomerulonephritis compared with patients diagnosed with interstitial nephritis, pyelonephritis, nephrosclerosis, diabetes mellitus, polycystic kidney, and miscellaneous renal diseases (P < 0.01, chi 2). There was a higher prevalence of HCV antibodies in patients with creatinine clearance lower than 30 mL/min (13%) compared with patients with creatinine clearance higher than 30 mL/min (2.7%) (P < 0.01, chi 2). These data suggest that HCV infection may be associated with the pathogenesis of glomerulonephritis. Alternatively, glomerulonephritis or severe renal insufficiency may increase the likelihood of HCV infection.