We performed a retrospective study to find out the frequency, clinical and pathological characteristics of membranoproliferative glomerulonephritis (MPGN) in Korean adults. Of the total 1,893 adults with biopsy-proven glomerulonephritis over the 13-year period from 1979 to 1991 in Seoul National University Hospital, there were 212 cases of MPGN of whom 22 had primary MPGN and 190 secondary MPGN. Secondary MPGN was composed of 64 cases of hepatitis B virus- associated glomerulonephritis(HBV-GN), 121 cases of lupus nephritis(LN) and 5 cases associated with other conditions. Age at diagnosis(median and range in years) was higher in primary MPGN(31, 16-67) and in HBV-GN (39, 16-60) than in LN(28, 16-44)(P<0.05). Male-to- female ratio was 1.2:1 in primary MPGN, 7.5:1 in HBV-GN and 1:13 in LN. At the time of diagnosis, nephrotic syndrome and azotemia were more frequent in primary MPGN(72%, 50%) and in HBV-GN (50%, 42%) than in LN(25%, 15%)(P<0.05). Decreases of C3 and CH50 were more common in LN(59%, 77%) than in primary MPGN(24%, 41%) or in HBV-GN(12%, 32%)(P<0.05). On light microscopic exams, tubular atrophy was more frequently observed in primary MPGN(96%) than in HBV-GN(57%) or in LN(69%)(P<0.05). Under immunofluorescence microscopy, mesangial deposition of IgM was more common in HBV-GN (50%) and in LN(59%) than in primary MPGN(6%) (P<0.05). The prognosis was better in LN(13 remission, 15 persistence, 1 end stage) than in primary MPGN(1 remission, 8 persistence, 4 deterioration, 6 end stage) or in HBV-GN(18 persistence, 4 deterioration, 2 end stage)(P<0.05). Conclusively, in Korea considering much higher incidence of secondary MPGN than that of primary MPGN contrary to western countries and the difference in prognosis between the primary and secondary forms, one should consider the possibility of secondary MPGN, especially hepatitis B virus- associated glomerulonephritis and lupus nephritis in adult patients diagnosed as MPGN by kidney biopsy in Korea.