ACUTE and chronic diarrhoea are both very common complaints in first-opinion small animal practice. Diarrhoea is defined as an increase in the frequency, fluidity or volume of faeces. It is a primary sign of intestinal disease, although it may also be a manifestation of other systemic diseases. Diarrhoea can occur as a consequence of small or large intestinal disease, but it is not uncommon for both to be present. Information gained from the clinical history can aid differentiation between diarrhoea of large and small intestinal origin. This article focuses on the acute presentation, although the differential diagnoses do overlap with chronic diarrhoea. It reviews the causes and sets out an approach to the investigation and management of patients. As well as discussing what treatments may or may not be appropriate, it gives some guidance on what to do if an infectious aetiology, such as parvovirus, is suspected.