Intestinal obstruction secondary to displacement of a stone from the gall bladder into the intestinal tract is relatively uncommon. The commonest site of calculus impaction is at the ilio-caecal valve. Occasionally, however, the gall stone may either pass through the valve into the colon or perforate directly into the transverse colon and impact in the distal colon. The extruded calculus is often only faintly calcified and may be difficult to identify on plain radiographs. We describe a case where multislice computed tomography of the abdomen enabled an accurate diagnosis to be made. Prompt surgical treatment was subsequently undertaken. We report the imaging findings with particular emphasis on the importance of computed tomography in establishing the diagnosis.