The most frightening complication following colorectal surgery is the anastomotic leakage which is associated with an high mortality rate, and the analysis of risk factors for the anastomotic leak is of great interest. The aim of this retrospective study is to evaluate the risk factor for the anastomotic leakage in personal series of patients who underwent colorectal surgery. We have analyzed a consecutive series of 1290 patients who underwent colorectal open surgery from 1970 to 2004. The associations between anastomotic leak and several risk factors were studied by univariate analysis. The variables considered were the following: age; sex; type of disease; elective or emergency surgery; type of surgery; type, design and site (intra or extra peritoneal) of the anastomosis; stapled or manual anastomosis; distance from anal verge of the colorectal anastomosis; intraoperative complications; protective stoma. The rate of anastomotic leakage was 4.8% (62/1290 patients). Significant factors were: the type of surgery (higher risk after restorative proctocolectomy or rectal resection), the site extra peritoneal of the anastomosis, the type of the anastomosis (higher risk after coloanal or ileal-pouch anal or colorectal), the stapled anastomosis, the intraoperative complications. After colorectal anastomosis the risk of leakage has progressively higher for low, ultra-low and coloanal anastomosis. In these conditions a protective stoma seems to be suitable.