Between December 1964 and April 1974, 216 renal transplants were performed on 200 recipients at the University Clinic of the Cantonal Hospital at Zurich. The ureteroneocystostomy was performed in most cases, a pyeloureterostomy being done only five times. 12% of all recipients (24 patients) developed serious urological postoperative complications involving 27 (14.3%) of the transplants, with four cases being fatal. Not considered as a serious complication were urinary infections and retention due to clotting, both of which could be treated conservatively with success. Of the more serious cases, 8 involved stenosis of the ureter, 4 compression of the ureter, 2 obstruction of the ureter, and 4 bladder fistulation. In 10 of these cases the complication can be related to imperfect operative technique in respect to transplanting the donor kidney. Preserving sufficient ureter vascularization is of paramount importance, and consideration must be given to increased vulnerability to infection as a result of the immunosuppressive therapy. Extreme stripping of the pyelon and ureter can result in stenosis and necrosis of the ureter. The treatment of urinary passage complications has not been standardized. However, fistula closure and operative correction of ureter obstruction must be carried out quickly.