Voiding dysfunction is a common sequel of abdominoperineal resection of the rectum. Twenty patients symptomatic after abdominoperineal resection, 14 with a preoperative normal urodynamic study and six with evidence of obstruction, were studied postoperatively. The importance of the following factors is analyzed: sex, stage, grade, size, distance of the tumor from the anal verge, metastatic lymph-node involvement, and extent of lymphadenectomy. Male gender, tumors situated between 4 and 8 cm from the anal verge, and lymphadenectomy that includes more than ten nodes may be considered risk factors for neurologic damage and postoperative voiding dysfunction.