A complication of colonic diverticulosis, giant diverticula are seen above all in the sigmoid region. On the basis of a case involving the transverse colon, the authors stress the clinical and ultrasonographic pseudo-tumoural symptomatology as well as the degree of superinfection of the contents. Anatomical arguments would be in favour of pathogenesis by progressive increase in size of an ordinary diverticulum rather than by perforation with secondary encystment. Excision of the diverticulum required segmental colectomy.