A retrospective population-based study was performed to describe the incidence rate of first time symptomatic urinary tract infection in children under 6 y of age. A total number of 299 children was identified during the 20-month study period in a population of 20,000 girls and 21,000 boys. The cumulative incidence rate during the first 6 y of life was 6.6% for girls and 1.8% for boys. The annual incidence rate in girls of urinary tract infection/1000 at risk was between 9 and 14 for each of the six 1-y age intervals. In girls, the proportion of febrile urinary tract infection was high during the infant year, while girls older than 2 y most often had non-febrile infection. For infant boys, the incidence rate and the proportion of febrile urinary tract infection were comparable to that of girls, while after the first year of life urinary infection of any kind was rare, with an incidence rate of 1-2/1000 at risk.