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Impairment in communication is a primary diagnostic feature of autism spectrum disorders (ASD), however relatively little is known about the early communication development of children with ASD. Vocalizations, which typically begin to emerge within the first year of life, are therefore an area of communication prime for research as a potential behavioral marker of ASD which can be assessed early in life. The purpose of this study was to compare differences in the vocalizations of children between 18 and 24 months of age later diagnosed with ASD (n = 50), a mentally and chronologically age-matched group of children with developmental delay (DD; n = 25), and a chronologically age-matched group of children with typical development (TD; n = 50). In addition, for children with ASD, concurrent and predictive relationships between vocalizations and developmental level were investigated. Precise measures of vocalizations were obtained through systematic observation of videotaped behavior samples from the Communication and Symbolic Scales Developmental Profile (Wetherby & Prizant, 2002). Children with ASD used significantly fewer vocalizations and a lower proportion of vocalizations with consonants than children with TD. In addition, children with ASD used a significantly higher proportion of atypical vocalizations than children with TD and a significantly higher proportion of distress vocalizations than both children with TD and DD. For the ASD group, the frequency of vocalizations and the frequency of vocalizations containing recognizable speech sounds correlated significantly with developmental levels in both the second and third years. In addition, communicative vocalizations late in the second year were found to uniquely predict expressive language outcome at age 3 over and above noncommunicative vocalizations. Overall, the results of this study indicated that by 18 to 24 months of age many vocalization measures significantly differentiate children with ASD from children with TD, with a higher proportion of distress vocalization differentiating children with ASD from both children with TD and DD. The importance of communicative vocalizations for later language development is highlighted by the results of this investigation. This study will contribute to the understanding of early vocal communication in children with ASD and assist in early identification.