Problems with social anxiety are frequently reported in people with autism spectrum disorders (ASD). It is possible that social anxiety, when present, exacerbates the experience of hostility and other forms of aggression in relation to ASD symptoms. This study sought to determine if social anxiety symptoms mediate the relationship between features of ASD and feelings of hostility in young adults. Self-report measures of social anxiety, ASD, and facets of aggression were collected in a non-clinical sample (n = 618) of college students. Social anxiety was found to partially mediate the relationship between ASD features and self-reported hostility. There was also evidence for inconsistent mediation, such that social anxiety dampened the strength of the relationship between ASD symptoms and verbal and physical aggression. Findings highlight the potential influence of associated psychiatric symptoms in people with ASD. In addition, dimensional conceptualization of ASD symptoms, as opposed to a categorical approach solely, may be a useful approach to studying complex personality processes.