Abstract
Rectal duplication cysts account for 4% of all duplications of the alimentary tract. Presentation in adulthood is rare. An asymptomatic 54-year-old man was referred for endoscopic colorectal cancer screening. A bulging mass covered by normal mucosa was identified in the rectum. Endoscopic ultrasonography (EUS) with fine needle aspiration (FNA) was made for a diagnosis of rectal duplication cyst. The patient was operated and the diagnosis was confirmed. The diagnosis of the rectal duplication cyst is a challenge. EUS may have a singular role when identifying a muscular layer, because this is the only absolutely necessary criterion for the diagnosis. FNA by EUS may eventually identify colorectal and/or heterotypic epithelium that are the other diagnostic criteria of the duplication cyst.