The term acute abdomen refers to signs and symptoms of abdominal pain, tenderness, nausea and vomiting, with or without the signs of local or diffuse peritonitis and systemic ilness, a clinical presentation, that often requires emergency surgical therapy. This review provides a framework for understanding abdominal pain, so that practitioners may determine those patients who need a more expedited evaluation. In the first part of the article, a general approach to the patient is outlined. Details in clinical examination and diagnostic possibilities are highlighted aswell. The pathways of visceral and somatic pain are described and signs of peritonitis are listed. From among diagnostic methods, laboratory tests, ultrasound and computer tomography are the most important ones for determining the reason of acute abdomen. The second part of the article describes the most frequent causes of acute surgical abdomen: peritonitis, ileus, bleeding, acute mesenteric ischemia, cholecystitis, peptic ulcer perforation, acute pancreatitis, appendicitis and diverticulitis.