Aim: Information about the prevalence of special diets in preschool children is limited. The aim of this study was to measure the prevalence of all special diets among preschool children in a Swedish municipality.Methods: This was a population-based cross-sectional survey of all 3276 preschool children aged one to five years in the municipality of Karlskrona, Sweden. The questionnaire assessed the number of children at each preschool, how many were on special diets, their dietary requirements, age, sex, whether they had a medical certificate and whether the special diet had a perceived medical cause. Results:We obtained data for 3221 (98%) of the children, and 19% had special diets, including 12% on nonmedical diets and 6.3% on medical diets. The five most common diets were avoiding pork (7.8%), a vegetarian diet (4.8%), and avoiding cows' milk (3.5%), hens' eggs (1.2%) and lactose (1.1%). Gluten avoidance was more common in girls than boys (0.8% versus 0.2%, p = 0.032). Half (47%) of the children on special medical diets lacked a medical certificate.