We successfully saved a patient with appendicitis followed by necrotizing fascitis. A 77-year-old man with a history of ambulatory treatment for depression underwent an emergency operation because of severe abdominal pain. Laparotomy demonstrated that necrotizing appendicitis was massively extending over the abdominal cavity, involving the right paracolic sulcus and Douglas pouch and posterior surface of the right kidney. Irrespective of the emergency surgery, redness and swelling in the right chest and abdomen, which was noted at the time of admission, was not decreased. Successively, a retension incision was performed under the diagnosis of necrotizing fasciitis. Necrotizing fasciitis is an extremely rare complication of appendicitis, and there were only 10 cases documented. Once necrotizing fasciitis occurs, the mortality rate is high, so that correct diagnosis and prompt debridement are mandatory. Particularly for elderly patients with appendicitis, rapid and accurate diagnosis and treatment are required.