A 73-year-old woman visited our hospital because of increasing abdominal distension and lower abdominal pain. On abdominal computed tomography (CT), hepatic portal venous gas (HPVG) and pneumatosis intestinalis of the small intestine were found. HPVG caused by intestinal necrosis was diagnosed, and an emergency laparotomy was thus performed. Necrosis of the small intestine over a 40-cm area from the ileocaecal region toward the mouth was found, and the lesion was resected. Histopathologically, haemorrhagic necrotic enteritis was diagnosed. The patient is alive as of the seventieth day after operation. The prognosis of intestinal necrosis accompanied by HPVG and pneumatosis intestinalis is poor. The presence of HPVG suggests the occurrence of a serious lesion in the abdominal cavity. Therefore, appropriate treatment should be performed immediately.