There is preliminary evidence that infant siblings of children with Autism Spectrum Disorder (ASD) have an atypical pattern of cry, characterized by higher fundamental frequency and increased dysphonation. This prospective study collected multiple cry samples of 12-month old siblings of children with ASD (n = 22, "high-risk" group) and 12-month olds with no family history of ASD (n = 27, "low risk" group). While there was no difference between groups in the fundamental frequency or degree of phonation of the cry samples, the duration of each cry unit was significantly shorter in the high-risk siblings (p < 0.05). The six infant siblings who received a diagnosis of ASD at age two had amongst the shortest recorded cry durations.