Microfibrils are a common component of connective tissue that have been described only rarely in the renal glomerulus. Structurally, microfibrils are fibrotubules with an average diameter of 12 nm, a lucid core, and a dark periphery. High resolution electron microscopy, including stereo microscopy performed on renal biopsy tissues, demonstrated the presence of microfibrils under the endothelium of the capillary walls and in the mesangium in several glomerular diseases. These diseases were characterized by widening of lamina rara interna or separation of the endothelium from the basement membrane, among them transplant glomerulopathy, focal segmental glomerulosclerosis (including a case associated with Marfan syndrome), preeclamptic toxemia, and less frequently hemolytic-uremic syndrome and malignant hypertension. The number of microfibrils generally correlated with the degree of subendothelial widening.