The transverse size of the kidneys was measured by CT, and CT findings of the kidneys were studied in 94 patients with chronic renal failure under hemodialysis (HD), 58 patients with chronic renal failure not under hemodialysis (CRF) and 100 controls. The transverse size of the kidneys decreased according to the deterioration of renal function. The ratio of the maximal renal transverse size to the minimal vertebral size, which the author proposed as a new criterion for renal atrophy, was 1.8 in controls, 1.2 in CRF and 0.8 in HD. A kidney smaller than the vertebral body indicated chronic renal failure. Characteristic CT features in CRF were mild renal atrophy and cystic changes (41.4%). In HD, renal atrophy was more advanced, the occurrence of cystic changes was more frequent (64.9%), and there were frequent renal (68.1%) and aortic calcifications. Furthermore acquired cystic disease of the kidney (ACD) was observed (27.7%) only in HD. In this study no renal neoplasm was found in ACD. However, several complications in HD, one perirenal hematoma and six hydronephroses, were observed.