Tailgut cyst (cystic hamartoma) is a congenital malformation that is typically found in the presacral (retrorectal) space, a remnant of the postnatal hindgut. The lining may be columnar, squamous, or transitional. The rectal wall is rarely involved. We present a case of a submucosal lesion in the descending colon of a 69-year-old man, which is morphologically consistent with tailgut cyst but is peculiar for its location in the descending colon and involvement of the submucosa. It is important for clinicians and pathologists to be aware of these unusual lesions as complete excision is curative, and malignant transformation can rarely occur.