Twenty-five cases of minimal change nephrotic syndrome(minimal change disease, MCD) with mesangial IgA deposition were evaluated electron microscopically. The thickness of the glomerular basement membrane(GBM) was 3875 ± 1271 A and 3056 ± 1201 A in adults and children, respectively. Alteration of the GBM was noted in 3 adults and eight children: splitting in 4, focal thinning in one, widening of the lamina rara interna in 10, and widening of the lamina rara externa in 4 cases. Minimal mesangial electron dense deposits were found in all but one adult, and an increase of the mesangial matrix and minimal mesangial proliferation were observed in 8 and 6 cases, respectively. Electron microscopic findings show representative findings of MCD in our cases. A relationship between the GBM alterations in these cases and frequent association of hematuria is suggested and discussed.