† The ureters and bladder are liable to injury during surgical operations on other structures within or about the pelvis. How this can happen is shown in nine case histories, six of them involving hysterectomy, one a lumbar laminectomy, one a colpotomy with transection of the uterosacral ligaments, and one a cesarean section. The surgical treatment of the individual cases was successful, but more important are the means to be used in preventing such injuries. A catheter should be inserted during operations near a ureter, to aid in identifying and avoiding it. If it is ligated, severed, or otherwise injured, it should be repaired at the time. If there is danger of kinking, a soft ureteral catheter can be left in place four to six days postoperatively. Urinary symptoms developing after a pelvic operation require prompt and precise diagnosis. This is usually not difficult, once the possibility of this complication is borne in mind.