The English and French literature on Capgras' syndrome yielded 315 patients, 212 of whom provided the basis for review. Forty-six percent presented with an affective disturbance. Seven variant forms of a unified delusion of substitution are described: Capgras; subjective doubles, Capgras type; Fregoli; intermetamorphosis; subjective doubles, autoscopic type; "reverse" subjective doubles; and "reverse" Fregoli. Classes of single and multiple forms of the delusion with either functional or organic etiology were compared. Multiple form classes had a greater diversity of variant forms.