To estimate the magnitude and distribution of self-reported, acute gastrointestinal illness in a Canadian-based population, we conducted a retrospective, cross-sectional telephone survey of approximately 3500 randomly selected residents of the city of Hamilton (Ontario, Canada) from February 2001 to February 2002. The observed monthly prevalence was 10% (95% CI 9·94–10·14) and the incidence rate was 1·3 (95% CI 1·1–1·4) episodes per person-year; this is within the range of estimates from other developed countries. The prevalence was higher in females and in those aged <10 years and 20–24 years. Overall, prevalence peaked in April and October, but a different temporal distribution was observed for those aged <10 years. Although these data were derived from one community, they demonstrate that the epidemiology of acute gastrointestinal illness in a Canadian-based population is similar to that reported for other developed countries.