Cold-knife incision of stenoses in the transplant ureter was performed in 11 patients with upper urinary tract obstruction in renal transplants. The operations were complicated by bleeding in 2 patients and the graft had to be removed in 1 of them. The stenoses could be treated successfully in 10 of the 11 patients (91%) and the mean serum creatinine concentration decreased significantly from 3.4 to 1.8 mg./dl. After a mean of 26 months only 1 obstruction recurred, so the long-term success rate was 82%. Because of the favorable long-term results and the low incidence of complications, we recommend endo-urological cold-knife incision of ureteral stenosis as the first-line treatment for upper urinary tract obstruction in renal transplants.