We report three patients who developed pseudomembranous colitis following aortic aneurysm resection. Colonic ischaemia can occur after such surgery and ischaemic colonic mucosa is known to be more susceptible to damage by bacteria and their toxins. This colonic ischaemia together with the antibiotic prophylaxis used may render aortic aneurysm patients susceptible to pseudomembranous colitis. It is important to distinguish pseudomembranous from ischaemic colitis in these patients as specific and effective drug therapy can be given to those with the pseudomembranous type.