Peritonitis (i.e. acute inflammation of the peritoneum) from appendicular origin, can be due to acute appendicitis or be observed after appendicectomy. Diagnosis is based on physical examination. Imaging procedures (ultrasound and computed tomography) are particularly useful in localized and postoperative peritonitis. Management includes surgery, antibiotics and intensive care. Early surgical treatment by appendicectomy represents the best way to improve the prognosis of the disease. Mortality is mainly observed in case of delayed diagnosis and in aged patients.