The clinical presentation, initial laboratory and renal biopsy findings, and course of focal segmental glomerulosclerosis (FSGS) were studied retrospectively in 57 children in order to compare findings in those with and without nephrotic syndrome and to establish factors of prognostic significance. All patients had proteinuria. Eleven patients were otherwise asymptomatic, and nephrotic syndrome did not develop (group 1); 14 patients had asymptomatic proteinuria, but nephrotic syndrome subsequently developed (group 2); 32 patients had nephrotic syndrome (group 3). There were no differences between these three groups with regard to sex, age, initial renal function, incidence of hypertension and hematuria, and pathologic findings. At the latest follow-up, five group 1 patients, six in group 2, and 14 in group 3 had chronic renal failure; the incidence was similar for those with asymptomatic proteinuria and those with nephrotic syndrome. The location of the sclerosis within the glomerulus proved to have prognostic significance. All 12 patients with peripheral FSGS maintained normal renal function, whereas in 25 of the 44 with hilar FSGS chronic renal failure developed.