Prospective questionnaire data from a longitudinal population sample on children with autism spectrum disorders (ASD), developmental delay, specific language impairment, or typical development (TD), were collected at ages eight, 12 and 24 months, via the Communication and Symbolic Behavior Scale Developmental Profile (CSBS)--Infant Toddler Checklist, and the Actions and Gesture section of the MacArthur-Bates Communicative Development Inventory (CDI):Words and Gestures. The four groups were compared at four years of age to identify whether any early behaviours differentiated the groups. While children with ASD differed from TD children on most social communicative measures by 12 months of age, the only social communication characteristic which could differentiate the children with ASD from the other groups were gesture scores on the CDI at 12 months and the CSBS at 24 months. Significant markers of ASD were identifiable in this community sample at an early age, although discrimination between clinical groups was rarely evident. (Contains 7 tables.)