Ureteral injury is one of the possible complications of distal colectomies. It may be caused by misidentification of the anatomic landmarks during the left lateral dissection, due to factor pertaining to the patient, the disease, and the surgeon. The only way to reduce the risk of this avoidable complication is the perfect knowledge and identification of the anatomy of the left ureter. In this article, we describe an anatomic triangle that can be a valid help in the identification of the ureter in the area where higher is the risk of iatrogenic injury. The left ureteric triangle can be prepared after the dissection of the left Toldt plane, as soon as the dissection reaches the superior mesorectum. Sides of this triangle are (a) superiorly, the dissected mesosigmoid, (b) right side, upper mesorectum and sacral promontorium, and (c) inferiorly, the margin of the incised posterior parietal peritoneum. The left ureter runs within this triangle.