Rectal implantation cysts can be caused by continued growth in the submucosa of traumatically misplaced columnar epithelium during previous surgery. Cases of implantation cyst occurring at the site of anastomosis have rarely been reported. Rectal implantation cysts occurring at an anastomosis site after a low anterior resection for rectal cancer need to be distinguished from locally recurrent rectal cancer. Here we present a case of rectal implantation cysts in a patient with rectal cancer who underwent laparoscopic low anterior resection 9 months previously. The diagnosis was made according to the characteristic image findings of endoscopic ultrasonography and enodsocopic ultrasonography-guided fine needle aspiration. This is the first case report of rectal implantation cyst in Korea. (Korean J Gastrointest Endosc 2010;40:382-386)