Acute segmental enteritis, also called "enteritis necroticans" is characterized by nonocclusive intestinal ischemia in the absence of any precipitating cause. We studied 30 such patients over a 5.5-year period. All patients had acute abdominal symptoms requiring emergency laparotomy, and in only 30% was a preoperative diagnosis of segmental enteritis proposed. The jejunum alone (63.3%), or with the ileum (26.7%), was the most common site of necrotic patches (86.7%), frank gangrene (50.0%), free perforation (36.7%), and circumferential dusky lesions (30.0%). Twenty-eight patients required resection of the affected bowel. Specimen angiography in two cases showed normal mesenteric vasculature. In 12 patients, a detailed microbiological profile from peritoneal fluid, intestinal contents, and intestinal wall was performed, but Clostridium welchii was isolated from none. The resected intestinal specimens showed mucosal ulceration, submucosal edema, mixed inflammatory infiltrate, and patchy necrosis of the muscularis propria. The intramural vessels were patent in all cases. Wound-related complications occurred in 14, pulmonary complications in 14, renal failure in eight, and fecal fistulas in five; 23.3% died.