Purpose.To describe the epidemiology of invasive pneumococcal infections in Canadian children 0 to 12 years old.Methods.At each of nine urban centers, active surveillance was conducted to identify all cases of invasive pneumococcal infection in children during 1994 to 1998. Postal codes were used to distinguish cases resident in defined urban areas from referral cases. Census data were obtained for each defined area to calculate age-specific incidence rates. Features of population-based cases were described.Results.From an average defined population of ∼1 million children, 937 eligible cases arose. Those 6 to 17 months old had the highest average incidence rate of 98.6/100 000/year. The average cumulative risk of infection was 1 in 460 between birth and 59 months, by which age 92% of cases had occurred. Among cases younger than 2 years of age, simple bacteremia accounted for 66%, pneumonia with bacteremia accounted for 14.7% and meningitis accounted for 11% (average incidence rate, 9.0/100 000/year). An underlying illness was present in 16% of all cases. The mortality rate was 1.8%.Conclusions.Invasive pneumococcal infections are relatively common in early childhood, based on 5 years of data from nearly 20% of the Canadian population ages 0 to 12 years. These data will be valuable for calculating the economic case for universal infant vaccination with newly available vaccines.