Background: Necrotizing soft tissue infection is a rare and aggressive medical and surgical emergency characterized by intense and severe tissue destruction, rapid onset systemic toxicity, and high mortality. Diverticulitis is a common complication of diverticular disease. However, its presentation as necrotizing soft tissue infection is rare. It is always important to identify the precipitating cause of necrotizing soft tissue infection to assist in appropriate treatment and risk stratification. Case Presentation: The patient was an 84-year-old female with a history of hypertension and chronic obstructive pulmonary disease with long-term steroid dependency. She presented to the emergency department with abdominal tenderness, left abdominal wall cellulitis, crepitus, and septic shock. Abdominal and pelvic computed tomography findings showed intra-abdominal abscess secondary to perforated sigmoid diverticulitis with abdominal wall abscess and necrotizing soft tissue infection of abdominal wall, chest wall, groin, and back. After intravenous fluid resuscitation and antibiotics, the patient underwent urgent laparotomy. She was found to have a large abdominal wall abscess, perforated sigmoid diverticulitis, and extensive necrosis of the torso extending from the groin to chest wall including the back. Conclusion: Abdominal wall necrotizing soft tissue infection is an uncommon complication of perforated diverticulitis. In an elderly immunocompromised patient with septic shock, perforated diverticulitis, and necrotizing soft tissue infection, the prognosis is poor.