In addition to confirming the established light microscopic findings, electron microscopic assessment of renal tissue with pyelointerstitial reflux damage also provides other important information. Isolated tubular epithelial cells and small tubular epithelial cell complexes, the earliest formative phase of thyroid-like lesions, were observed after subtotal tubular destruction. Moreover, secretory granule-like structures, identified by immunohistologic methods as renin granules, were found in tubular epithelium, apparently atrophic and cell-rich glomeruli, and walls of tortuous arterioles. Various stages of glomerular scarring were documented in the early phase of glomerular destruction and electron-dense material (IgM) was identified. Electron microscopy plays an important role in differentiating thin-walled vessels (lymphatic vessels, capillaries, venules). While the presented findings are characteristic for reflux nephropathy, they are not pathognomonic: they also occur, for example, in urinary tract obstructions without reflux mechanism.