PURPOSE: The purposes of this study are to determine the incidence of postoperative ileus after colorectal surgery, to analyze its clinical features, and to identify the risk factors for its development. METHODS: We reviewed the cases of 263 patients with mechanical ileus among 3,237 patients who underwent colorectal surgery in our clinic between June 1989 and December 2000. RESULTS: A total of 263 (8.1%) patients of postoperative ileus were documented, 193 (73.4%) cases occurred during the 1st. year. Postoperative ileus is influenced by the initial site of surgery; the rectum has more impact than the colon (P=0.028). The causes of postoperative ileus were adhesion, recurrence of cancer, and parastomal hernia. Adhesion (81.1%) was the most common cause of ileus, and cancer recurrence (18.0%) was the second. However, in postoperative ileus requiring surgery, cancer recurrence increased with time (2 year: 58.1%). The cases receiving postoperative adjuvant radiation therapy presented a significant increase in the incidence of postoperative ileus (10.3% vs 6.7% P=0.01) and in the requirement for surgical treatment (4.6% vs 2.7%, P=0.04). Patients with a temporary stoma presented a significant increase in the incidence of postoperative ileus than patients with a permanent stoma (P=0.001). The frequency of prior episodes of ileus was the strongest predictor of recurrence. CONCLUSIONS: There is a high risk of adhesion-related problems after colorectal surgery. The risk factors are associated with rectal surgery, postoperative radiation therapy, and a temporary stoma.