The proposed project aims to evaluate the feasibility and acceptability of a novel behavioral intervention, Infant-Toddler Years Pivotal Response Treatment (ITY-PRT), designed to enhance the frequency of communication and social engagement in infant siblings of children with Autism Spectrum Disorders (ASD; SIBSASD). Genetic studies reveal that SIBSASD are at risk for a variety of developmental challenges, with a significantly increased risk for ASD (Bailey, Phillips, & Rutter, 1996) and other social, cognitive, and language difficulties (Bailey et al., 1995; Bolton et al., 1994). Given the high genetic risk, prospective studies of infant SIBSASD have beeninitiated in order to elucidate the developmental processes in ASD and enhance early identification. Emerging research indicates that symptoms of ASD may be present as early as 12 months of age (Rogers, 2009). While we are not yet able to differentiate children at 12 months of age who will ultimately develop ASD from those with other developmental delays or transient issues, these children warrant intervention based on their risk status and clinical presentation. Thus, prospective studies at the Yale Child Study and other major research centers around the country are documenting the early emergence of the symptoms of ASD and identifying infants who are likely to face developmental challenges and warrant referrals for clinical services as early as 12 months of age. However, there is currently a paucity of empirically-supported interventions available for infant SIBSASD, urging the need to design developmentally appropriate interventions for at-risk infants. In synergy with the ongoing prospective studies for infant SIBSASD at the Yale Child Study Center (PI: Katarzyna Chawarska), we will pilot ITY-PRT, a downward extension of Pivotal Response Treatment (PRT). PRT is an empirically supported intervention for children with ASD and is documented by the National Research Council (NRC) as one of 10 comprehensive intervention models for ASD (NRC, 2001). Utilizing a randomized-controlled group design, 30 infant SIBSASD who demonstrate significant delays in communication and/or social interaction at 12-15 months of age will be randomly assigned to receive either ITY-PRT in addition to a standard referral to community treatment, Treatment As Usual (TAU), or assigned to receive TAU only. ITY-PRT will consist of five hours/week of parent education (including two hours of group parent education, and three hours of individual sessions) over the course of six months. Outcomes will be focused on the feasibility and acceptability of this program, including measures of attendance, utilization of intervention procedures outside of intervention sessions, and overall parent satisfaction. We will also evaluate the preliminary efficacy of ITY-PRT by analyzing the frequency of child communication, child social interaction behaviors, and parental bids for communication during parent-child interaction probes, as well as changes in standardized measures of development and social behavior both from pre to post and across treatment and control groups.