Two siblings born from consanguineous parents experienced infantile nephrotic syndrome with ocular and neurological abnormalities and a micropenis in the boy; both patients died before age 1. The opportunity to perform successively a renal biopsy and a two-step binephrectomy permitted a good histological follow-up. The lesions were characterized by mesangial involvement, followed by an extensive extracapillary proliferation and tubular dilatations with a high mitotic activity of the epithelium with anisocaryosis; the main features consisted in major ultrastructural changes of the glomerular basement membrane which were more significant and different from those previously described in the diffuse mesangial sclerosis. These 2 cases may either constitute a new entity or an extreme form of diffuse mesangial sclerosis, supported by recessive autosomal inheritance.