Large bowel obstruction (LBO) is associated with high morbidity and mortality due to delayed diagnosis and/or treatment. MDCT has become the standard of care to identify the site, severity, and etiology of obstruction. The goal of this review is fourfold. The first objective is to give clues to differentiate LBO from colonic pseudo-obstruction. The second objective is to describe CT features in the most common cause of LBO which is colonic cancer by illustrating classical and atypical features of colonic cancer responsible for LBO and by giving the features which must be reported when differentiating malignant from benign: presence of local lymph nodes, other colic localizations, length of involved segment, presence of diverticula, or other. The third objective is to illustrate the various causes of LBO which can mimic a colon cancer by leading to a thickening of the colonic wall: diverticulitis, ischemic colitis, endometriosis, inflammatory disease and to give tips which permit to evoke another diagnosis than a colon cancer in patient with a LBO and a thickening of the colic wall. The fourth objective is to describe the common signs of cecal and sigmoid volvulus and to give tips for a diagnosis sometimes difficult particularly for cecal volvulus: one of two transition points according to the type of volvulus and the presence of a whirl sign with a torsion of the mesenteric vessels.