Infections of the gastrointestinal tract and liver are the most common disorders of the alimentary tract in both the industrialized and in the resource-poor countries of the world. Although diarrhoea is the most common manifestation of gastrointestinal infection, there are several other important clinical syndromes, including oesophagitis, gastritis, intestinal obstruction and proctitis and perianal disease. Enteric fever is primarily a systemic bacter-aemic infection with a gastrointestinal portal of entry and with important intestinal complications. Bacterial and parasitic infections of the liver and biliary tract are also a major cause of morbidity and mortality worldwide, producing liver abscess, cholangitis and biliary obstruction and chronic liver disease with portal hypertension. Infections such as tuberculosis and schistosomiasis produce, in the small and large intestine, inflammatory lesions which frequently progress and heal with marked fibrosis. Many bacterial and viral infections cause relatively mild illnesses in immunocompetent individuals and will be cleared spontaneously without the use of antibiotics.