Patients undergoing long-term dialysis are subject to cyst formation, hemorrhage, and neoplasia in their native kidneys. Detection of these complications with incremental dynamic CT and detection with sonography were compared prospectively in 41 patients (79 kidneys) who had been undergoing dialysis intermittently for 3 or more years. Acquired cystic kidney disease (five or more cysts per kidney) was identified in 59% of kidneys by use of CT and in 18% by use of sonography. CT showed a complete renal contour definition in all cases, sonography did so in only 57%. Three solid renal tumors (2- to 4-cm diameter) were identified with both techniques with no false-negative evaluations. Four benign hemorrhagic cysts were identified with combined CT (hyperdense mass) and sonography (benign cysts). CT provided the best anatomic image quality and was mor accurate for detection of acquired cystic kidney disease. CT and sonography were equivalent for detection of solid tumors. Our results suggest that dynamic contrast-enhanced CT scanning with the supplemental use of sonography is the best imaging regimen for the evaluation of suspected acquired cystic kidney disease and its potential complications.