The authors encountered an uncommon case of a retroperitoneal T-shaped duplication that presented with a communication with the descending colon, descending downward along the descending colon posterolaterally, passing through the sigmoid mesocolon and across the midline at the level of L5 to S1 vertebrae, ascending behind the ascending mesocolon, and terminating beneath the third portion of the duodenum. Using a 3-port transperitoneal laparoscopic technique, the duplication was completely resected. On reviewing the literature, T-shaped duplication has occurred in only 4 cases; and all arose from the colon and were not associated with other anomalies. Dense adhesions between the blind end and surrounding tissues, a retroperitoneal location, and the U-shaped loop of the duplication appear to support the theory that it was the result of persistent neurenteric canal during the formation of the alimentary tract before the normal midgut-positioning process.