Capgras delusion is the belief that significant others have been replaced by impostors, robots or aliens. Although it usually occurs within a psychiatric illness, it can also be the result of brain injury or other obviously organic disorder. In contrast to patients with prosopagnosia, who cannot consciously recognize previously familiar faces but display autonomic or covert recognition (measured by skin conductance responses), people with Capgras delusion do not show differential autonomic activity to familiar compared with unknown faces. This challenges traditional models of the way faces are identified and presents some epistemological questions concerning identity. New data also indicate that, contrary to previous evidence, covert recognition can be fractionated into autonomic and behavioural/cognitive types, which is consistent with a recently proposed modification of the modal face recognition model.