There is limited information on the causes of paediatric diarrhoea in Sydney. This cross-sectional study used clinical and microbiological data to describe the clinical features and pathogens associated with gastrointestinal illnesses for children presenting to two major public hospitals in Sydney with diarrhoea, for the period January 2007-December 2010. Of 825 children who tested positive for an enteric pathogen, 430 medical records were reviewed. Adenovirus, norovirus and rotavirus were identified in 20.8%, 20.3% and 21.6% of reviewed cases, respectively. Younger children were more likely to have adenovirus and norovirus compared with rotavirus (P=0.001). More viruses were detected in winter than in the other three seasons (P=0.001). Rotavirus presented a distinct seasonal pattern with the lowest rates occurring in the warm months and peaking in the cooler months. Adenovirus showed a less consistent monthly trend, and norovirus detection increased in the cooler months (P=0.008). A decline in the number of rotavirus cases was observed after mid-2008. The majority of childhood diarrhoeal illnesses leading to hospital presentations in Sydney are caused by enteric viruses with most infections following clear seasonal patterns. However, a sustained decrease in the incidence of rotavirus infections has been observed over the study period.