AbstractA case of squamous cell carcinoma arising in a cystic duplication within the small bowel mesentery of a 65‐yr‐old man is described. The cyst wall had a double layered smooth muscle coat with intervening ganglionic plexus; part of the cyst was lined by ciliated columnar epithelium.Twelve previously reported cases of carcinoma arising in duplications are reviewed together with the present case. In all but one case, the onset of symptoms was probably related to malignant change; the age at presentation ranged from 26 to 65 yrs. Pre‐operative diagnosis proved difficult, and led to a delay in the appropriate treatment of some of the five cases involving duplications of the rectum.Duplications of the alimentary tract are encountered only occasionally in adults; malignant change, although rare, should be recognised as a possible complic