Aim:The aim of the present study was to describe intraoperative underwater colonoscopy (IUC) and recommend the use of this new technique in emergency settings for the management of acute left-sided colonic obstruction. Patients and Methods: IUC was performed with a laparoscope attached to a video-camera system after in-sleeve, on-table colonic irrigation. The colon was transected proximally to the tumour, and a nylon camera drape was sutured tightly to the proximal colonic end. Following colonic irrigation, the washout was stopped, and IUC was accomplished by introducing a laparoscope into the bowel. Finally, the laparoscope was withdrawn and formal surgery was performed. Results: IUC was successfully used in nine patients who underwent emergency colon surgery; eight patients had colonic obstructions due to adenocarcinomas, and one patient had colonic perforation. IUC revealed three synchronous lesions in the obstructed colonic segments which one of them was an adenocarcinoma in three patients. Another patient had a polyp located distally to the tumour, which was determined preoperatively. Primary resection and stapling anastomosis were performed in all cases. Postoperative complications were atelectasis and delay of intestinal motility in two patients; both recovered well. There was no complication due to IUC or primary operation; for example, anastomotic leakage or wound infection. During the follow up, one patient died 10 months after primary operation due to a cardiac event. Conclusion: IUC following in-sleeve, on-table irrigation is safe and quick to perform, and enables the assessment of colonic mucosa with good visibility. This method was found to be helpful to perform intraoperative colonoscopy when indicated in the emergency surgery of the obstructed left-sided colon when conventional endoscopy was not available at the theatre.