Background Psychiatric conditions, notably anxiety, commonly co-occur with autism spectrum disorders (ASD). Method This study investigated self-reported behavioural, cognitive and affective symptoms of social anxiety (SA) in 50 adult males with ASD. Associations between SA, core ASD symptoms and facets of neuropsychological functioning were also examined. Results Twenty-six participants (52%) endorsed levels of SA that exceeded the suggested caseness threshold for social anxiety disorder. Categorical and dimensional data analyses indicated that there were no relationships between SA symptoms, present-state or childhood ASD symptom-severity, or measures of socio-emotional processing in this sample. Conclusions Study findings suggest that severity of SA is not merely a reflection of ASD symptom-severity. Further research is needed to ascertain the prevalence of SA in adult ASD epidemiological samples, and identify causal and maintaining mechanisms for these co-morbid symptoms.