The increasing recognition of the benefits of early intervention for children with autism spectrum disorder (ASD) stresses the importance of early identification of children who might benefit from those programs. However, in the early years of life it may be difficult to distinguish children with ASD from children with other developmental disorders. The aim of the present study was to identify behavioural patterns that could facilitate this differentiation. Prior to diagnostic assessment, 2- and 3-year-old children (n=30), all referred to a clinic for "possible autism", were observed in a semi-structured play interaction, and their parents were interviewed about the children's early development from 0 to 24 months. Following diagnostic assessment, the 17 children fulfilling the ICD-10 criteria for ASD were compared to the 13 children diagnosed with other developmental disorders (outside the autism spectrum). On the basis of parent reports only a few distinguishing signs of ASD were found before 24 months of age. On the basis of professional observations in a semi-structured play interaction several distinguishing signs were found for the 2- and 3-year-olds; smiles in response, responds to name, follows pointing, looks to "read" faces, initiates requesting verbal and nonverbal behaviours, and functional play.