Infants with older siblings with Autism Spectrum Disorders (ASD-sibs) are at risk for socioemotional difficulties. ASD-sibs were compared to infants with typically developing older siblings (TD-sibs) using the face-to-face/still-face (FFSF) at 6 months and the Early Social Communication Scale (ESCS) at 8, 10, 12, 15, and/or 18 months. ASD-sibs smiled for a lower proportion of the FFSF than TD-sibs and lacked emotional continuity between episodes. With respect to TD-sibs, ASD-sibs engaged in lower rates of initiating joint attention at 15 months, lower rates of higher-level behavioral requests at 12 months, and responded to fewer joint attention bids at 18 months. The results suggest subtle, inconsistent, but multi-faceted deficits in emotional expression and referential communication in infants at-risk for ASDs.