PURPOSE:To identify the risk factors for anastomotic leakage after left‐sided colorectal resections with rectal anastomosis.METHODS:Forty‐four patients with anastomotic leakage identified from a computer‐generated database were compared with 44 control patients standardized for gender, age, and operative indication.RESULTS:The mean hospital stay was significantly prolonged in the leakage group, which resulted in a higher total cost of hospital treatment. The preoperative variables significantly associated with anastomotic leakage included malnutrition, weight loss, hypoalbuminemia, cardiovascular disease, two or more underlying diseases, and use of alcohol. The surgery‐related factors that turned out to be significant were The American Society of Anesthesiologists physical status, operation time greater than two hours, multiple blood transfusions, intraoperative contamination of the operative field, and a short distance of the anastomosis to the anal verge. Obesity, body mass index, diabetes, smoking, serum hemoglobin, serum creatinine, serum bilirubin, bowel preparation, mode of antibiotic prophylaxis, type of anastomosis, technique of stapling, size of stapler used, and use of drain were nonsignificant variables. Malnutrition, weight loss, use of alcohol, intraoperative contamination, long operation time, and multiple blood transfusions remained significant in logistic regression model. Eighty‐six percent of the patients with three or more risk factors of anastomotic leakage belonged to the leakage group.CONCLUSIONS:Patients with multiple risk factors have higher risk for anastomotic leakage. When patients have three or more risk factors, the creation of a protective stoma should be considered in cases with a low rectal anastomosis, and all these patients should be carefully monitored postoperatively for signs of possible leak.