To investigate the incidence, pathophysiology and clinic determinants of persistent diarrhoea (more than seven days) after childhood gastroenteritis, we prospectively evaluated 168 consecutive patients admitted to the Royal Children's Hospital, Brisbane, with gastroenteritis. Thirty-two children (19%) developed persistent diarrhoea; only two-thirds of them had an identifiable aetiological factor, including di- or monosaccharide intolerance (31%), persisting or suspected pathogen (22%) and cow's milk protein intolerance. Computer aided analysis of risk factors in the preceding enteritis showed this complication to be more frequent in young age groups (P less than 0.01) where the patient was less than 10th percentile for weight (P les than 0.02); in Aboriginals (P less than 0.01); where there was a history of previous diarrhoea (P less than 0.001), delayed hospital admission (P less than 0.001) and antibiotic/antidiarrhoeal usage (P less than 0.05); and where there was a bacterial pathogen (P less than 0.001). Severity and outcome were variable with most cases requiring a defined formula diet. These findings provide some insight into the problem of persisting diarrhoea after gastroenteritis, aid identification of at risk patients, and suggest guidelines for management and prevention.