Background: Hyalinized renal arterioles (Hy) can be counted per unit area of PAS-stained paraffin sections. The percentages of nephrons having hyalinized afferent and efferent arterioles can be assessed in serial sections. Methods: Slides of renal tissue were assessed for Hy in 559 basal forensic autopsies, i.e. those with no condition known to correlate with hypertension. Serial sections in a series of 20 cases were used to measure afferent and efferent arterioles and determine formulas to relate afferent and efferent arterioles to Hy. The formulas were used in the 559 cases to assess the trends on age of Hy in terms of percentage of affected nephrons. Results: Hy increased rapidly from ages 15 to 34 years, but stabilized from ages 35 to 102 years at levels implying afferent arterioles of about 2/5 of nephrons and efferent arterioles of about 1/5. Most of the nephrons in the kidney were deduced to be supplied by hyalinized afferent arterioles in nearly half of all subjects from ages 35 to 102 years, and the rates were the same at all ages. Conclusion: These data provide for the first time provisional estimates for the prevalence of Hy to be used as baselines for biopsy comparisons. Failure of numerous kidneys to enter end-stage nephrosclerosis in spite of several decades of involvement by hyalinization in half or more of their arterioles does not support the view that hyalinization induces ischemic nephron atrophy.