The occurrence rate of renal cell carcinoma is significantly higher in the native kidneys of patients undergoing chronic hemodialysis than in kidneys of normal subjects. These carcinomas may be difficult to detect because these kidneys tend to be small and distorted owing to acquired cystic disease. Four cases of renal cell carcinoma detected by CT are presented (three in patients undergoing chronic hemodialysis, and one in a patient with a functioning transplant who had history of dialysis). All kidneys had extensive acquired cystic disease. In two cases, contrast-enhanced scans showed a solid lesion of lower density than the kidney. In another case, in which IV contrast material could not be given, the mass was of higher density than the kidney and retroperitoneal lymphadenopathy was present. In the fourth case, no distinct solid mass could be identified. The only sign of malignancy in this case was extensive lymphadenopathy. Whenever CT examination of the abdomen is performed in a patient undergoing chronic hemodialysis, the kidneys must be evaluated carefully because of the increased frequency of renal cell carcinoma. In a few cases, a distinct solid lesion may not be apparent or may be subtle owing to distortion of renal anatomy by acquired cystic disease.