PURPOSE: The complication after colostomy formation may place undue hardship and emotional trauma on the ostomates. The purpose of this study was to find the effect of preoperative stoma site marking on postoperative stoma related complication. METHODS: We recruited 127 colostomy patients who underwent sigmoid or descending end colostomy, by elective operation. Transverse colostomy, loop colostomy, and emergency operation were excluded in this study. We divided the patients into two groups according to pre-operative stoma site marking by an enterostomal therapist. Postoperative stoma related complications were compared and analysed prospectively using chi-square test and paired t-test. Significance was assigned to a P value of < 0.05. RESULTS: Among 127 patients, 49 were marked preoperatively (marking group) while 78 were not marked (non- marking group). Overall stoma related complications were developed in 32 (25%) cases. Major complications including prolapse, parastomal hernia, stenosis were developed in 10 (8%) cases and minor complications including peristomal dermatitis and wound infection were developed in 22 (17%) cases. Stoma related complications were developed in 7 (14%) cases in the marking group and 25 (32%) cases in the non-marking group (P<0.05). Major complications were developed in 2 (4%) cases in the marking group and 8 (10%) cases in the non-marking group. Minor complications were developed in 5 (10%) cases in the marking group and 17 (22%) cases in the non-marking group. However, the difference in major and minor complications between the groups was not statistically significant. Of minor complications in the non-marking group, 9 (53%) cases due solely to postoperative frequent stool leakage caused by inappropriate location of the stoma. However, in the marking group, postoperative stool leakage was not observed. CONCLUSIONS: Preoperative stoma site marking by an enterostomal therapist may reduce postoperative stoma related complication. All elective procedure that result in stoma formation should be assessed and marked preoperatively.