Congenital nephrotic syndrome of the Finnish type (CNF) is well characterized in infants and associated with major lipid risk factors for atherosclerosis. This study was undertaken to investigate if any arterial pathology is present in children with CNF and, if so, to describe its nature in renal arteries collected at nephrectomy at a mean age of 12.5 +/- 4.4 months. Denuded endothelial injury and intimal thickening were seen in 9 out of 10 patient specimens of renal arteries. Intimal thickening contained loose abundant extracellular matrix with a few smooth muscle or myofibroblastoid cells. Only a few Sudan black- or oil red O-positive lipid droplets were found in six and seven samples, respectively. Areas immunoreactive with antibodies against apoprotein B were seen in only two specimens. Immunohistochemistry did not reveal any activated T or B cells, or any expression of IL-1 or IL-2 receptors. Macrophages were present in only two specimens. No foam cells were seen. We conclude that the vascular pathology together with altered lipoprotein metabolism indicates that children with CNF might be at risk for early atherosclerotic arterial disease, particularly if their hyperlipidemia persists.