To date, the biological basis of autism spectrum disorders (ASDs) remains unknown. Thus, identification and diagnosis are reliant on behavioral presentation and developmental history. There have been significant advances in our knowledge of the early signs of ASD through the use of retrospective videotape analysis, parental report, screening studies, and more recently, studies on high-risk infant siblings. Despite behavioral markers being identified within the first year of life, the current average age of diagnosis for ASD remains at approximately 3 years or older. Consequently, these children are not receiving intervention in their early years, which is increasingly recognized as an important time to begin intervention. There remains little research on the prospective identification of these children in a community-based sample before 18 months. It is recommended that future prospective studies monitor behavior repeatedly over time, thereby increasing the opportunity to identify early manifestations of ASD and facilitating the charting of subtle behavioral changes that occur in the development of infants and toddlers with ASD.