We report 4 patients with glomerulonephritis (GN) associated with hepatitis C virus (HCV) infection seen between August 1993 and July 1996. Two of them were male and median age was 41 years. Anti-HCV was detected by enzyme-immunoassay and HCV-RNA by PCR. Serum cryoglobulins, 24-hour proteinuria, and erythrocyte dismorphism were also determined. Viremia, cryoglobulinemia, hematuria and proteinuria were observed in all patients. Liver biopsies revealed inflammatory activity in 3 cases, and renal biopsies revealed membranoproliferative glomerulonephritis in 3 patients and mesangial proliferative glomerulonephritis in 1 patient. Two patients are on specific therapy for HCV infection (IFN in combination with ribavirin) and have presented clinical and laboratory improvement. The occurrence of active liver disease and viremia concurrent with urinary alterations suggests viral involvement in renal disease, a conclusion supported by the by improvement of urinary alterations observed after treatment for HCV. We conclude that the search for viral markers in patients with GN is important since their detection could change the therapeutic approach.