Infectious and inflammatory enterocolitides can present with an acute abdomen. The most common entities are ulcerative colitis, Crohn disease, and Clostridium difficile colitis. This article reviews the clinical and imaging findings of patients who present acutely with infectious and inflammatory enterocolitides. The acute abdomen can be defined as the sudden onset (generally <24 hours) of severe localized or generalized abdominal pain that prompts the patient to seek immediate medical assistance; most often a visit to the emergency department.