50% of the patients admitted for acute abdominal pain have an infectious intra-abdominal disease, most of them an appendicitis, a cholecystitis or a diverticulitis. These infectious diseases are due to a noninfectious lesion of the wall of an intestinal organ. The defense mechanism and the bacterial synergism limit the number, nature and local extension of the multiple micro-organism, producing a strong selection. For the treatment, antibiotics play an important adjuvant role. The main question in all cases is to determine if the cure of the wall lesion is necessary. Furthermore, it is important to choose the ideal time to do it, according to the extension of the lesion, the immunocompetence and the physiological state of the patient. The advantages and inconveniences of an early or late operation have to be weighted. Some special aspects of appendicitis, cholecystitis and diverticulitis are discussed.