Diffuse mesangial sclerosis (DMS) has been described as a distinct morphological pattern observed in patients presenting with a congenital or infantile nephrotic syndrome (NS) leading to end stage renal failure (ESRF) before the age of 3 years (Habib & Bois: Helv. Peadiat. Acta 28: 91-107, 1973). In recent years, we diagnosed this entity in 36 infants and we wish to report our findings which extend our previous observations. The nephropathy was discovered before 1 year of age in 26 patients. In one of these the onset was neonatal. Five additional children were between 1 and 2 years of age at onset of the disease and the remaining 5 were between 24 and 42 months old. Thirty-three patients presented with a NS often preceded by a proteinuria and associated with renal failure in 6 of them. The 3 remaining patients presented with renal failure. Thirty-one patients reached ESRF before the age of 4 years. Progression was slower in 5 patients who were respectively 5, 5, 6, 8 and 11 years old at ESRF. Thirteen patients were transplanted and none recurred their original disease. Seven patients in 4 families had similarly affected siblings. In 16 patients (6 boys and 10 girls) the nephropathy was isolated. In the remaining 20 several associated findings were noted. In 14 infants a diagnosis of Drash syndrome was made on the basis of the association of a male pseudo-hermaphroditism (PsH) and Wilms tumour (WT) in 5, of a male PsH in 5 additional infants and of a WT in 4 female patients.(ABSTRACT TRUNCATED AT 250 WORDS)