Many treatment programs for individuals with an autism spectrum disorder (ASD) target social skills, and there is growing attention directed toward the development of specific interventions to improve social skills and social interactions in this population (Hestenes & Carroll, 2000; Strain & Hoyson, 2000). However, there are limited tools available to assess social skills in children with ASD. Furthermore, there are even fewer designed to assess response to intervention. The focus of the current study was to examine the convergent, criterion, and incremental validity of a new measure designed to assess the development of social interaction skills in individuals with ASD; namely, the Behavioral Assessment of Social Interactions in Young Children (BASYC; Gillis, Callahan, & Romanczyk, 2010). A total of 44 individuals with ASD participated in this study (mean age was 7 years 11 months; range was 2-12 years old). The BASYC demonstrated convergent validity with the Social Approach subscale of the Pervasive Developmental Disorders Behavior Inventory (PDDBI; Cohen & Sudhalter, 2005) and criterion-related validity with the Socialization domain of the Vineland Adaptive Behavior Scales-II (VABS-II; Sparrow, Cicchetti, & Balla, 2005). One of the two BASYC subscales demonstrated incremental validity over the PDDBI in predicting variability in the VABS-II Socialization domain. The results of this research provide further support for the clinical utility of the BASYC as a measure of social interaction skills in individuals with ASD. (Contains 3 tables.)