<h2>Abstract</h2> Almost every individual suffers at least one episode of acute diarrhoea each year. Worldwide, diarrhoeal diseases are second only to cardiovascular diseases as a cause of death, and in some parts of the world they account for more years of potential life lost than all other causes combined. In the UK, diarrhoea is the most common illness after the common cold; acute diarrhoeal illnesses account for about 10% of all visits to general practitioners and incur substantial time lost from school and work. Diarrhoea is a complex, multifactorial entity with many causes. Many diarrhoeal illnesses are acute, mild to moderate, of brief duration and self-limiting; in such cases, individuals do not seek the advice of a doctor and usually deal with the illness themselves using over-the-counter remedies, by modifying their diet, or by doing nothing. Medical help is usually sought when diarrhoea is more severe, lasts for more than a few days, is accompanied by fever or rectal bleeding, or results in prostration. There are several diagnostic tests. Many are expensive, time-consuming and invasive, so a systematic approach is essential to make an accurate diagnosis without subjecting the patient to unnecessary investigations.