This study examined social communication profiles from behavior samples videotaped between 18 and 24 months of age in three groups of children: 50 with autism spectrum disorders (ASD), 23 with developmental delays (DD), and 50 with typical development (TD). The ASD group scored significantly lower than the DD group on 5 social communication measures and the TD group on all 14 measures, indicating distinct profiles late in the second year. Understanding was the strongest predictor of developmental level and behavior regulation and inventory of gestures were the strongest predictors of autism symptoms at 3 years of age. The predictive relations suggest five pivotal skills late in the second year that have a cascading effect on outcomes of children with ASD.