Early communication impairment is among the most-reported first concerns in parents of young children with autism spectrum disorder (ASD). Using a parent-report questionnaire, we derived trajectory groups for early language and gesture acquisition in siblings at high risk for ASD and in children at low risk, during their first 2 years of life. Developmental skills at 6 months were associated with trajectory group membership representing growth in receptive language and gestures. Behavioral symptoms also predicted gesture development. All communication measures were strongly related to clinical and developmental outcomes. Trajectory groups further indicated slowest language/gesture acquisition in infants with later ASD diagnoses, in particular when associated with language delay. Overall, our results confirm considerable variability in communication development in high-risk infants.