Background: Capgras’ delusion has captured psychiatrists’ imaginations, but the clinical features of the delusion have rarely been studied and presented systematically. Aims: The present study systematically reviews all case reports on Capgras’ delusion in the English language in order to better understand differences between organic and functional aetiologies. Methods: All medical and psychiatric databases were searched, as were the bibliographies of published case reports, narrative reviews, and book chapters. Results: A total of 258 cases were identified from 175 papers. Functional Capgras’ delusion was more associated with a wider variety of imposters; multiple imposters; other misidentification syndromes; auditory hallucinations; other delusions; and formal thought disorder. Organic cases were associated with age; inanimate objects; memory and visual-spatial impairments; right hemispheric dysfunction; and visual hallucinations. Executive dysfunction and aggression were associated with both types. Conclusions: Specific features of the -Capgras’ delusional content and associated signs point to either organic or functional aetiology. The delusion is more amorphous than many theorists have supposed, which challenges their explanatory models.