Folie à deux

Folie à deux (/fɒˈli ə ˈduː/; French pronunciation: ​[fɔli a dø]; French for "a madness shared by two"), or shared psychosis, is a psychiatric syndrome in which symptoms of a delusional belief and hallucinations are transmitted from one individual to another. The same syndrome shared by more than two people may be called folie à trois, folie à quatre, folie en famille or even folie à plusieurs ("madness of many"). Recent psychiatric classifications refer to the syndrome as shared psychotic disorder (DSM-IV) (297.3) and induced delusional disorder (F.24) in the ICD-10, although the research literature largely uses the original name. The disorder was first conceptualized in 19th-century French psychiatry by Charles Lasègue and Jean-Pierre Falret and so also known as Lasègue-Falret Syndrome.