Forty cases of focal sclerosing glomerulonephropathy with nephrotic syndrome or proteinuria were studied retrospectively in regard to clinical presentation, response to steroid therapy and clinical course, and histopathology of the lesion. Morphologically there was a focal segmental and global sclerosis with subendothelial hyaline deposits, collapse of the capillary loops, intracapillary hyaline material or foam cells, filling and widening of the mesangium with mesangial matrix, focal tubular atrophy, and focal interstitial fibrosis. Thirty-four patients had been treated with prednisone; initial complete remission of the nephrotic syndrome occurred in only 4 patients and partial remission in 10. Nine of these 14 patients had nephrotic relapse or became resistant to steroids. Thirty-three percent of the patients progressed to end-stage renal failure and an additional 25 percent had impairment of renal function after a mean of 8 years from onset. Three patients received kidney allografts, and in two the disease recurred in the transplanted kidney. Focal sclerosing glomerulonephropathy associated with nephrotic syndrome or proteinuria appears to be a clinicopathologic entity characterized by resistance to steroid treatment, frequent progression to end-stage renal disease, and recurrence in the transplanted kidney.