A 61-year-old man experienced cardiopulmonary arrest twice during treatment for diabetic ketoacidosis and hyperosmolar hyperglycemic syndrome.He was successfully resuscitated with intensive treatment.Subsequently, anemia progressed and a fecal occult blood test was positive.Ischemic enteritis with multiple small ulcers in the cecum and deep ulcers in the ileum were observed with lower gastrointestinal endoscopy.Approximately 1 week after the examination, melena and intestinal obstruction developed.Fever and abdominal pain were intensified, and blood test findings markedly worsened and abdominal CT showed that the small intestine was dilated, the wall of the terminal ileum was thickened, and a small amount of ascites in the pelvis.Laparotomy was performed 32 days later.The wall of the terminal ileum was markedly thickened.Intestinal necrosis and perforation were observed in a segment of approximately 10 cm that was 5 cm proximal to the terminal ileum.Ileocecal resection and ileostomy were performed.We encountered a patient who experienced cardiac arrest during treatment for hyperosmolar hyperglycemic syndrome and diabetic ketoacidosis, developed necrotic ischemic enteritis with circumferential perforation, and required surgical treatment.