We investigated discrepancies between parent- and self-reported social functioning among youth with autism spectrum disorders (ASD). Three distinct samples showed discrepancies indicating that parents viewed their children as performing one standard deviation below a standardization mean, while youth viewed themselves as comparably-skilled relative to peers. Discrepancies predicted lower parental self-efficacy, and lower youth-reported hostile attributions to peers, marginally-lower depression, and decreased post-treatment social anxiety. Discrepancies predicted outcomes better than parent- or youth-report alone. Informant discrepancies may provide valuable additional information regarding child psychopathology, parental perceptions of parenting stress, and youth treatment response. Findings support a model where abnormal self-perceptions in ASD stem from inflated imputation of subjective experiences to others, and provide direction for improving interventions for youth and parents. (Contains 5 tables.)