The incidence, pathogenesis, diagnostic procedures and management of surgical and urological complications observed in 437 consecutive renal transplantations are described. Urinary fistulas (4.3%) and ureteral obstructions (1.8%) are the most important urological complications. Prompt diagnosis and correction are mandatory to prevent graft loss and death of the recipient, especially if these complications are associated with infection. A high incidence of reflux into the graft (37.6%) was detected by routine cysto-urethrogram. For the first time a correlation between the incidence of reflux and the number of rejection episodes could be demonstrated, suggesting immunological alterations of the transplant ureter as the main pathogenetic factor of reflux after renal transplantation. However, reflux does not seem to be deleterious to graft prognosis, provided there is no subvesical obstruction. The main surgical complications after renal transplantation are lyymphoceles (8.2%), renal artery stenoses (6.7%), and spontaneous graft ruptures (4.3%), while wound infections (1.8%) and arterial thromboses resp. ruptures (0.7% resp. 0.5%) are rare complications. Urological and surgical complications can be kept to a minimum by strict adherence to certain principles in pretransplant recipient evaluation, donor nephrectomy (in situ perfusion, en bloc nephrectomy) and the technique of graft implantation. The extravesical technique of uretero-neocystostomy is the procedure of choice for the reconstruction of the urinary tract in renal transplantation.