The effacement of podocyte foot processes is a well-known phenomenon occurring in many glomerulonephritides with proteinuria. The fundamental sign of IgA nephropathy is hematuria, but proteinuria also frequently occurs. The authors measured the extent of foot process effacement in 100 IgA nephropathy cases with proteinuria and correlated it with the amount of proteinuria. The extent of foot process effacement was greater in the nephrotic proteinuria group than in the subnephrotic proteinuria or control groups. The degree of foot process effacement was positively correlated with proteinuria. This study demonstrates that proteinuria in IgA nephropathy is closely related to foot process effacement.