Capgras' syndrome, one form of the delusional misidentification syndromes, is described. Three patients with the syndrome are reported. The first had a right cerebral infarction, the second had nephrotic syndrome secondary to severe pre-eclampsia in the puerperium, and the third had uncontrolled diabetes mellitus with dementia. Evidence is reviewed regarding an organic aetiology for Capgras' syndrome. We conclude that, when the syndrome is present, a thorough search for organic disorder should be made.