Purpose: How do children with autism spectrum disorders (ASD) extend a noun to the category of objects it labels? Given their tendency to perceive locally, their extensions might be too narrow. Given their social-communicative deficits and a context in which the knowledge of a social-communicative partner promotes narrow extensions, their extensions might be too broad. Method: We tested these predictions by comparing 25 high-functioning school-aged children with ASD to 29 age-matched peers with typical development (TD) in a task that required extraction of commonalities of object referents and use of social-communicative context to support the category inference. Results: The children with ASD readily extended a given noun to multiple exemplars, thereby demonstrating tacit knowledge that words label categories and the ability to override local perceptual biases they might have. However, unlike their peers with TD, those who had concomitant weaknesses in semantic and syntactic language ability formed broad categories when their social partner's behavior suggested narrow categories. Conclusions: Some, but not all, people with ASD fail to use social context to support inferences about word extension. The direction of any causal relationship between failure to use social contextual cues and language deficits awaits determination.