The development of renal cysts appears to be a common feature of terminal renal failure in patients with diffuse renal parenchymal disease. In the present investigation, the kidneys of 13 patients with terminal renal failure but not receiving dialysis, of 14 patients on maintenance hemodialysis and of 4 patients after renal transplantation (patients' own kidneys) were studied by computed tomography. Cystic lesions in the contracted renal parenchyma could be demonstrated by computed tomography in 7/13 non-dialyzed patients with terminal renal failure, in 11/14 patients on maintenance hemodialysis as well as in 3/4 transplanted patients (patients' own kidneys). Both solitary cysts (10/21 patients) and multiple cysts (11/21 patients) were observed. The size varied from 0.5 cm (barely detectable) to 3 cm in diameter. Such cysts could also be demonstrated at autopsy. Possible clinical complications include spontaneous retroperitoneal hemorrhage, macrohematuria, matrix stone formation and formation of benign or malignant papilloma. The present study shows that computed tomography allows the detection of acquired renal cysts in uremic patients in vivo. The cysts appear prior to dialysis, seem to increase in frequency during dialysis and do not disappear after transplantation. The lesions can be distinguished from multicystic or polycystic disease.