A 60-year-old man was admitted to the hospital because of left-sided abdominal pain and diarrhea.The patient had been in stable health until three or four years earlier, when he began to have intermittent pain in the left flank that radiated to the left upper and lower quadrants, without a change in bowel habit. Evaluation included a colonoscopic examination, an intravenous urographic study, and a computed tomographic (CT) scan of the abdomen, which were negative. Three months before admission severe, diffuse abdominal pain occurred, and the patient was seen at another hospital. He passed fresh blood through the rectum frequently for the first 12 hours. Proctosigmoidoscopic examination was negative, and stool cultures yielded no pathogenic microorganisms. The patient was discharged after four days without a definitive diagnosis.Two months before admission colonoscopic examination at this hospital was negative. The patient was subsequently well except for bouts of minor pain in the left flank. Sixteen days before admission severe pain recurred on the left side of the abdomen and in the left flank. He was admitted to a second hospital, where his temperature rose to 39.2ºC, with evidence of peritoneal irritation. At laparotomy a thickened mesentery of the splenic flexure was observed; an intraoperative colonoscopic examination revealed ulcers in the same area. The splenic flexure was resected, and a temporary transverse colostomy was performed. Microscopical examination of the specimen obtained during the operation showed changes consistent with ischemic colitis. The postoperative course was prolonged by persistent fever, for which antibiotics were given, and he was discharged on the 13th hospital day.Two days before admission similar abdominal and left-flank pain recurred and worsened progressively. On the next day the patient passed several hard lumps of stool from the colostomy, followed by diarrheal stools, and late that evening he came to this hospital.The patient was an educator. He had never smoked, consumed little alcohol, and used no illicit drugs. An appendectomy had been performed many years earlier, and several bouts of pyelonephritis occurred before the age of 43 years, with negative evaluations of the urinary tract. He had undergone surgery for a hiatus hernia and the carpal tunnel syndrome. Idiopathic hypertrophic subaortic stenosis was discovered 12 years before admission, and a myomectomy was performed, with incomplete relief of symptoms. Eight years before admission the patient was treated for acute renal failure, which was ascribed to rhabdomyolysis of uncertain cause. Eight months before admission a dual-chamber electronic pacemaker was implanted for pacing from the right ventricular apex; he had no atrioventricular dissociation or other cardiac arrhythmias. His medications consisted of disopyramide, ciprofloxacin, and lorazepam. There was no history of recent rash, paresthesias, fever, chills, nausea, genitourinary symptoms, bleeding from the colostomy, postprandial pain or bowel emptying, or in...