Although alterations of emotion processing are recognized as a core component of autism, the level at which alterations occur is still debated. Discrepant results suggest that overt assessment of emotion processing is not appropriate. In this study, skin conductance response (SCR) was used to examine covert emotional processes. Both behavioural responses and SCRs of 16 adults with an autistic spectrum disorder (ASD) were compared to those of 16 typical matched adults. Participants had to judge emotional facial expressions, the age of faces or the direction of a moving object. Although behavioural performance was similar in the two populations, individuals with an ASD exhibited lower SCRs than controls in the emotional judgement task. This suggests that such individuals may rely on different strategies due to altered autonomic processing. Furthermore, failure to produce normal physiological reactions to emotional faces may be related to social impairments in individuals with an ASD.