The criteria now used in an attempt to distinguish irritable bowel syndrome from organic gastrointestinal disease rely almost entirely on symptoms of colonic origin. 'Non-colonic' symptoms, however, arising either from elsewhere in the gut or of a more general nature, are common in irritable bowel syndrome and may have even better diagnostic potential. The prevalence of these non-colonic features was assessed in 107 patients with the irritable bowel syndrome and 295 subjects with other gut disorders. Gastrointestinal type non-colonic symptoms are useful in differentiating irritable bowel syndrome from inflammatory bowel disease but, with the exception of early satiety, are not helpful when there is gastro-oesophageal or biliary disease. More general 'non-colonic' features, such as lethargy and backache, are much commoner in irritable bowel syndrome than in all the organic gastrointestinal diseases studied and have good discriminant function. Multiple logistic regression analysis identified certain features that had a particularly significant independent risk for irritable bowel syndrome. Those were lethargy (relative risk 6.7), incomplete evacuation (RR 5.2), age under 40 (RR 2.1), backache (RR 2.0), early satiety (RR 1.8), and frequency of micturition (RR 1.8). These relative risks can be multiplied together to give an overall risk when more than one of these features is present in a patient. Until a diagnostic test is available more confident diagnosis of irritable bowel syndrome can be achieved by identifying symptoms that have good discriminant function. The results of this study indicate that the non-colonic features of irritable bowel syndrome may be especially valuable in this respect.