[Les demoiselles de Rochefort, or a clinical illustration of madness in pairs].

Although folie à deux is a confidential entity that has disappeared from psychiatric textbooks and is disguised in current international classifications of mental disorders, which tend to obscure the fundamental notion of the dyad, recent case reports highlight the topicality of the disorder. The richness of the clinical encounter with twin sisters, presenting a common delusion of parasitic infestation, may prompt us to question the disorder differently, guided in particular by ancient writings and the analytic compass.