All patients referred for diarrhoea over a 2-year period were studied to determine the relative frequency of organic diarrhoea and functional disorder. One hundred and nine patients had diarrhoea of established aetiology at admission. Two hundred and one patients with diarrhoea of unestablished aetiology at admission were interviewed about symptoms, and faecal output was measured. An organic or other explanation was eventually found in 78 patients (39%), whereas the bowel symptoms were categorized as functional or transient in 58%. Chronic diarrhoea of unknown origin was seen in 3%. Only 40% of the patients referred for diarrhoea had faecal output greater than 200 g/day. A reliable differentiation between organic and functional diarrhoea based solely on history and a physical examination at admission was not possible, as the initial diagnostic guess was only confirmed in 42% of the patients. More sensitive and specific indicators of functional diarrhoea are needed before the patients can be safely classified without the need for thorough diagnostic study.