This study aims to explore the relationship between developmental ability, autism and adaptive skills in preschoolers. Adaptive function was assessed in 152 preschoolers with autism, with and without developmental delay, and without autism, with and without developmental delay. Their overall adaptive function, measured by the general adaptive composite on the Adaptive Behaviour Assessment System, was closely correlated to developmental ability as measured by the general quotient on the Griffith Mental Development Scales. Children with autism performed significantly less well on both scales. Domain scores discriminated between children with and without autism, with poorer performance on both the social and practical domain scores for children with autism, even when controlling for the effects of development. Children with average development, both with and without autism, had lower adaptive skills than expected for their developmental level. The importance of considering domain scores as well as the general adaptive composite when determining support needs is emphasised.