Giant diverticulum of the colon is a rare finding which has not so far been reported in the British radiological literature. A 66-year-old man was referred to hospital with a 24-hour history of abdominal pain and the passage of three melaena stools. Examination revealed some abdominal distension and tenderness, but no masses were felt. Bilateral inguinal herniae were noted for which a truss was worn. Sigmoidoscopy to a distance of 16 cm showed fresh melaena stool, but no mucosal lesion could be seen. First degree haemorrhoids were present, but these showed no sign of recent haemorrhage. A plain film of the abdomen revealed a large gas-filled “cyst” in the left lower quadrant (Fig. 1). The patient had a past history of a transthoracic vagotomy for obstructive airways disease, and repair of a ventral hernia. He had been under treatment with prednisone and various antibiotics for his chest condition. Barium enema examination revealed diverticular disease of the sigmoid colon. One of the diverticula measured ...