In a total of 283 biopsies, 100 (35%) were found to be IgA nephropathy. The incidence reached 40% among primary glomerulonephropathies. On the basis of histopathologic changes in glomeruli, these biopsies were classified into 3 groups. The criteria employed correlated well with clinical, laboratory and immunofluorescent findings. Immune complex pathogenesis was discussed in relation to our findings.