[Thorotrast kidney as a precancerous condition].

9 cases of "thorotrast kidney" after retrograde pyelography with reflux are presented. In 6 patients carcinoma of the renal pelvis developed 47--31 years after thorotrast pyelography. Because of this high rate of carcinoma induction, thorotrast kidney must be classified as a precancerous condition with high-rate tumor manifestation. Thorotrast kidney is diagnosed on X-ray by very opaque linear densities following the calices and pyelon. Early ureteronephrectomy is the treatment of choice in unilateral thorotrast kidneys. If uretero-nephrectomy is not possible, the patient should be followed up regularly with urinary cytologic examinations for early detection of malignancy.