The aim of this study was to determine the prevalence of gastroenteritis among children aged 4 years in South Australia. A cross-sectional survey of 9543 South Australian children aged 4 years was undertaken. Parents completed a questionnaire on behalf of their child who had attended a pre-school health check in 1998. The questionnaire covered gastrointestinal and respiratory symptoms experienced by the child in the previous 2 weeks and other risk factors for gastroenteritis. The 2-week prevalence of gastroenteritis among 4-year-old children was 14·2%. The major risk factors for gastroenteritis were presence of persons who had gastroenteritis inside the home, contact with persons who had gastroenteritis outside the home, antibiotic use and sore throat. Medical attention was sought for 20% of children who had gastroenteritis. Gastroenteritis is a significant cause of morbidity among young children and presents a considerable burden on the community. A substantial proportion of these occurrences of highly credible gastrointestinal symptoms may be manifestations of respiratory infections.