In this article the epidemiology, aetiology, neuroanatomy and neuropsychology of the Capgras syndrome (CS) are reviewed in detail. CS is characterized by the delusional belief that one or a few highly familiar people have been replaced by impostors who are physically very similar to the original/s. The patient acknowledges that the double and known person look alike, but maintains the belief that the significant person, in psychological terms, is absent. CS is relatively rare, occurring predominantly in the context of schizophrenia, and was traditionally considered to have its origins in psychodynamic conflict. More recently, however, it has been estimated that between 25 and 40% of cases are associated with organic disorders, which include dementia, head trauma, epilepsy and cerebrovascular disease. Neuroimaging evidence suggests a link between CS and right hemisphere abnormalities, particularly in the frontal and temporal regions. Neuropsychological research has provided empirical support for these findings, by consistently reporting the presence of impairments in facial processing--an established right hemisphere function. It is likely that the study of this symptom will lead to a greater understanding of the neurological basis of psychotic experiences and may provide a paradigm for how the psychoses should be investigated.