Clinico-histological features in 32 patients with nephrotic syndrome (NS) due to focal segmental glomerulosclerosis (FSGS) were examined. Thirteen (group A1 were diagnosed as cases of FSGS within 2 years of the onset of NS, and 8 (61%) showed progressive renal dysfunction. Ten (group A2) developed FSGS more than 2 years after the onset of NS and had a favorable prognosis. Nine (group B) differed from groups A1and A2 in that the remaining nonsclerosed glomeruli showed slight mesangial proliferation. All but 1 patient of group B developed FSGS within 2 years of the onset of NS, and the prognosis was poor. No patient studied showed a transition between groups A and B. In some patients, lipoid nephrosis preceded FSGS, in group A2. Thus, for an accurate prediction of the prognosis, FSGS should be divided into three subclasses, based on clinico-histological features.