Hepatitis C viral infection occurs relatively low in Korea compared to hepatitis B. However, it progresses into chronic hepatitis and cirrhosis more frequently than HBV. It may be associated with cryoglobulinemia and glomerulonephritis, both in native and transplanted kidneys. We report three cases of membrano-proliferative glomerulonephritis type I in anti-HCV positive, but cryoglobulin-negative patients, presenting massive proteinuria, two in native kidneys and one in an allograft. HCV-RNA was positive in sera of two patients. Two were cirrhotic and ALT was mildly elevated in two. In addition to the characteristic membranoproliferative feature, two native kidneys overlapped with features of diabetic nephropathy. Immunofluorescence demonstrated mainly IgM and C3 deposits along the peripheral capillary walls. Subendothelial electron dense deposits were present in the glomeruli of all three cases with subepithelial and intramembranous deposits in two. HCV-RNA was associated not only with a greater amount of immune deposits but also with subepithelial and intramembranous deposits, indicating the role of active infection.