Aim: To investigate the prevalence of children who are in need of special support in the total population of children attending preschools (CA 1–6) in two Swedish counties, and the functional problems exhibited by the children in relation to demographical and environmental factors in the preschool 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 support were undiagnosed children with functional difficulties related to speech, language and interaction with peers.

Conclusion: Undiagnosed and diagnosed children share the same type of difficulties. Thus, in estimating the prevalence of children in need of special support in a preschool context, traditional disability categories capture only a small proportion of the children experiencing difficulties. Therefore, a functional approach in studies of children in need of special support is recommended.