Food allergies (FAs) and hypersensitivities (FHSs) have rarely been studied in large unselected child populations. This population-based cross-sectional survey estimated the occurrence of FHS as perceived by parents and that of FA diagnosed by a physician among children aged 1-4 yr in south-eastern Finland. Before the scheduled annual follow-up visit to the local child health clinic, the parents of children who were born between 1 April, 2001 and 31 March, 2005, and living in the Province of South Karelia (data from Finnish Population Register) were mailed a questionnaire containing items on the child's background, physician-diagnosed FAs and FHSs perceived by the parents. The questionnaires were returned during the visit. Three thousand three hundred and eight (69%) out of the 4779 questionnaires were returned. The lifetime prevalence of physician-diagnosed FAs was 9%. In an additional 21%, FHSs were perceived by the parents only. In a further 19% at least one food item had been eliminated from the diet without any perception of symptoms, this proportion having a downward trend by age. Physician-diagnosed FAs were more common in boys than in girls. Cow's milk was the most commonly reported cause of food-associated symptoms (13% of all children). One-third of the children aged 1-4 yr suffered from food-associated symptoms, and in an additional fifth at least one food item had been eliminated from their diet, implying that every other child had possibly been subjected to some form of elimination diet.