Aim: To investigate the prevalence of children who are in need of special support in the totalpopulation of children attending preschools (CA 1–6) in two Swedish counties, and the functionalproblems exhibited by the children in relation to demographical and environmental factors in thepreschool context.Method: Survey distributed to (N = 1138) preschools in two Swedish counties.Results: The majority of children perceived by preschool teachers and in need of special supportwere undiagnosed children with functional difficulties related to speech, language and interactionwith peers.Conclusion: Undiagnosed and diagnosed children share the same type of difficulties. Thus, in estimating theprevalence of children in need of special support in a preschool context, traditional disability categories captureonly a small proportion of the children experiencing difficulties. Therefore, a functional approach in studies ofchildren in need of special support is recommended.