Toddler screening for autism spectrum disorders (ASD) has a tremendous impact on reducing the age of diagnosis, thereby increasing the time children with ASD can receive early intervention (EI). In turn, EI improves long-term prognosis in ASD. The American Academy of Pediatrics (AAP) recommends screening all toddlers for ASD at 18 and 24 months, yet implementation is far from universal, in part due to heavy demands during brief pediatric check-ups and other identified barriers. Efficacy studies have demonstrated that paper-and-pencil screening using one of the tools recommended by the AAP, the Modified Checklist for Autism in Toddlers (M-CHAT), coupled with the Follow-up questions, can successfully detect many toddlers with ASD at the 18- and 24-month check-ups. A revision (M-CHAT-R) improves sensitivity. When both M-CHAT(-R) and Follow-up are used in low risk samples, 93% show significant developmental delay, indicating high confidence that children who screen positive are in need of referral for evaluation and EI services. This study will validate an electronic 2-stage screening, integrating the M-CHAT-R with the Follow-up (M-CHAT-R/F) into an efficient tool that parents complete at home or in the pediatric office. The validation study will compare a sample of 5,000 toddlers screened via a secure website to a sample screened using the traditional delivery of paper M-CHAT-R and Follow-up by phone for toddlers showing ASD risk; the traditional sample will be selected from an ongoing NICHD-funded study. Screen positive cases will be offered a free diagnostic evaluation and will be referred to EI. Analyses will evaluate the utility of M-CHAT-R/F by comparing the number of children who screen positive, the positive predictive value, and the number of cases who decline the follow-up questions in each group. It is also predicted that the electronic group will show the added benefits of reduced delay to evaluation, increased participation in evaluation, and will report high levels of satisfaction with the M-CHAT-R/F. Following validation, the web-based M-CHAT-R/F will be disseminated to parents and practitioners. Web-based screening will have immediate public health impact by increasing availability of toddler screening and increasing confidence that screen positive cases warrant immediate referrals to EI and diagnostic evaluation.