Purpose: In this study, the authors aimed to examine the vocalizations of children with autism spectrum disorder (ASD) in the second year of life and their relationship to other areas of development. Method: Vocalizations were examined in 125 children between ages 18 and 24 months: 50 later diagnosed with ASD, 25 with developmental delays (DD) in which ASD was ruled out, and 50 with typical development (TD). Precise measures of vocalizations were obtained through coding of video-recorded behavior samples from the Communication and Symbolic Behavior Scales Developmental Profile (Wetherby & Prizant, 2002b). Results: The ASD group used a significantly lower proportion of vocalizations with speech sounds and a significantly higher proportion of atypical vocalizations than children with TD. The ASD group used a significantly higher proportion of distress vocalizations than the TD and DD groups. For the ASD group, the frequency of vocalizations with speech sounds correlated significantly with developmental levels both concurrently and predictively. In the ASD group, communicative vocalizations late in the second year were found to uniquely predict expressive language outcome at age 3 years above noncommunicative vocalizations. Conclusions: Further examination of distress vocalizations as a potential early indicator of ASD is recommended. In addition, the importance of early communicative vocalizations for later language development is highlighted. (Contains 6 tables and 1 footnote.)