The purpose of the present study is to determine how accurate an estimation may be made of classification and incidence of renal diseases in the old by pathological and epidemiological procedure. Three hundred and seventy-seven subjects were autopsied in Hisayama Study since its inception in the 10 years 1961 through 1971. We estimated the severity of arterial and arteriolar changes by quantitative measures and selected arterial and arteriolar nephrosclerosis by our-own criteria. In 23, 904 subjects of the annual autopsy cases in Japan, the pathological diagnosis of renal and urinary tracts diseases was found in 4, 009 cases. The results of Hisayama Study and Japanese annual pathological autopsies were compared; 1) As to the incidence of renal diseases in Hisayama nephrosclerosis was observed with the most frequency, in order interstitial nephritis. Meanwhile, interstitial nephritis, nephrosclerosis and glomerulonephritis were noted in this sequence in the annual collection of autopsies in Japan. 2) The cases with principal postmortem diagnosis of renal diseases in Japanese annual autopsiesies terminated to uremia in 1.3%-4.3%, which were mainly caused by glomerulonephritis in the younger, and by interstitial nephritis in the older. On the other hand, the renal disease was major factor in the death of the patients in 1.6% of the cases in Hisayama, but there was no glomerulonephritis. 3) The incidence of nephrosclerosis was increased with aging process, but malignant nephrosclerosis was not found in Hisayama, and decreased with aging in the Japanese annual autopsies. 4) Interstitial nephritis including pyelonephritis was most common renal disease in the autopsy material independently of aging, the most causes of which were upper urinary tracts infection due to obstruction, especially in the younger. 5) The most cases with renal infarcts of the old in Hisayama autopsies were due to arteriosclerotic diseases, otherwise in the annual collection of autopsies in Japan, renal infarcts was commonly arised from arteriosclerotic diseases in the older, and from endocarditis in the younger.