Peritoneal encapsulation is a rare congenital anomaly characterised by a thin membrane of peritoneum encasing the small bowel to form an accessory peritoneal sac. We present a case of peritoneal encapsulation diagnosed incidentally in an 82 year old man undergoing laparotomy for colonic cancer. The sac was easily excised and surgery was otherwise uneventful. A discussion of the case and a review of the literature are presented.