We investigated which item subsets of the Vineland-II can discriminate low-functioning preschoolers with ASD from matched peers with other neurodevelopmental disorders, using a regression analysis derived from a normative sample to account for cognitive and linguistic competencies. At variance with the typical profile, a pattern with Communication more impaired than Socialization was observed. The source of the frequently reported Socialization delay in ASD appears to be in Playing and Imitating skills only, not in other social adaptive behavior skills. The combination of item subsets Playing, Following instructions, Beginning to talk, and Speech skills provided the best discrimination between the two clinical groups. Evaluation of the Vineland-II score on item content categories is a useful procedure for a more efficient clinical description.