Capgras delusion is classified with the misidentification syndromes. In dementia it associates cognitive deficiency of memory and facial recognition (prosopoagnosia) with delirious idea of substitution by a double. The first reported case in the paper describes the important affective and comportmental reactions due to the identification of a double perceived as an imposter, affecting both the suffering person and his family. Rarely, as reported in the second case, misrecognition concerns the person itself (autoprosopagnosia) who can have the illusion to be in front of a twin brother (« auto-Capgras »). We discuss data from the literature concerning prevalence, results of cerebral imaging and functional prognosis associated with this curious syndrome.