OBJECTIVE: Despite behavioral markers of autism spectrum disorders (ASDs) being evident within the first year of life, there remains little research on the prospective identification of these children in a community-based setting before 18 months. The aim in the Social Attention and Communication Study was to identify infants and toddlers at risk of an ASD during their first 2 years. METHODS: A total of 241 Maternal and Child Health nurses were trained on the early signs of ASDs at 8, 12, 18 and 24 months. Using a developmental surveillance approach with a community-based sample, a cohort of 20,770 children was monitored on early social attention and communication behaviors. Those infants/toddlers identified as "at risk" were referred to the Social Attention and Communication Study team from 12 months for developmental and diagnostic assessments at 6 monthly intervals, until 24 months. RESULTS: A total of 216 children were referred, with 110 being further assessed. Of these, 89 children were classified with an ASD at 24 months, and 20 children had developmental and/or language delays, resulting in a Positive Predictive value of 81%. The estimated rate of ASDs in the Social Attention and Communication Study cohort ranged from 1:119 to 1:233 children. Estimated sensitivity ranged from 69% to 83.8%, and estimated specificity ranged from 99.8% to 99.9%. CONCLUSION: Developmental surveillance of social and communication behaviors, which differ according to the age at which the child is monitored, enables the accurate identification of children at risk for ASDs between 12 and 24 months. Education on the early signs is recommended for all primary health care professionals to facilitate early identification of ASDs.