Folie à deux
shared psychosis, a psychiatric syndrome in which symptoms of a delusional belief are transmitted from one individual to another
Folie à deux (French for 'madness of two'), also called shared psychosis or shared delusional disorder (SDD), is a rare psychiatric syndrome in which symptoms of a delusional belief are "transmitted" from one individual to another.
The disorder, first conceptualized in 19th century French psychiatry by Charles Lasègue and Jules Falret, is also known as Lasègue–Falret syndrome. Recent psychiatric classifications refer to the syndrome as shared psychotic disorder (DSM-IV – 297.3) and induced delusional disorder (ICD-10 – F24), although the research literature largely uses the original name. The same syndrome shared by more than two people may be called folie à trois ('three') or quatre ('four'); and further, folie en famille ('family madness') or even folie à plusieurs ('madness of several').
This disorder is not in the current, fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), which considers the criteria to be insufficient or inadequate. The DSM-5 does not consider shared psychotic disorder (folie à deux) as a separate entity; rather, the physician should classify it as "Delusional Disorder" or in the "Other Specified Schizophrenia Spectrum and Other Psychotic Disorder" category.
Signs and symptoms
This syndrome is most commonly diagnosed when the two or more individuals of concern live in proximity, may be socially or physically isolated, and have little interaction with other people.
Various sub-classifications of folie à deux have been proposed to describe how the delusional belief comes to be held by more than one person:
Folie imposée (imposed psychosis)
Where a dominant person (known as the 'primary', 'inducer', or 'principal') initially forms a delusional belief during a psychotic episode and imposes it on another person or persons (the 'secondary', 'acceptor', or 'associate'). Normally the latter, described as "un malade par reflet", does not suffer from a true psychosis. If the parties are admitted to hospital separately, the delusions in the person with the induced beliefs are typically abandoned.
This brief starts where responsible research should: with the source description of “Folie à deux” as shared psychosis, a psychiatric syndrome in which symptoms of a delusional belief are transmitted from one individual to another. Everything that follows is an evidence route, not borrowed authority.
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The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated May 27, 2026. The linked authority identifier is Q1435409. The Library of Congress control number is sh85049648. None of the 1 selected statements returned an explicit reference.
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This entry incorporates text from “Folie à deux” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.