The aim of this study was to determine whether high-resolution ultrasound is able to differentiate between the various diseases associated with nephrotic syndrome (NS). We reviewed the US features of 15 patients less than 1 year presenting a NS whose exact type was defined by pathology nephrotic syndrome of Finnish type (NSFT, n=2); focal and segmental hyalinosis (FSH, n=3); minimal-change glomerular disease (MCGD, n=2); neonatal glomerulonephritis (n=1), and diffuse mesangial sclerosis (DMS, n=7). The US features studied included the size of the kidneys, cortical echogenicity, cortico-medullary differentiation (CMD), and borders. The images were reviewed on hard copies by two observers unaware of the final diagnosis. In each case a diagnosis was proposed based on the reading of the US features. Six patients with DMS displayed a peculiar US pattern: mild increase of renal size; and inhomogeneous (patchwork-like) parenchymal hyperechogenicity that included areas of the cortex and medulla. The NSFT and neonatal glomerulonephritis displayed some of the same US features: increased kidney size (+2 SD) and had homogeneous cortical hyperechogenity with persistent cortico-medullar differentiation. The kidneys in the 3 patients with SFH were sonographically normal (n=1) or displayed a mild cortical hyperechogenicity (n=2). Inhomogeneous parenchymal hyperechogenicity involving only segments of the cortex and medulla seems to be a specific US pattern for DMS. Ultrasound is less specific for the other types of CNS.