A delusion may be shared by a small group of persons. This is referred to as "folie" (French for madness or lunacy).



(1) The presence of a situation generating strong emotions (death, loss, strife, etc.).

(2) The primary delusion is developed by a strong-willed individual of a group.

(3) Other members of the group share the same delusion (folie partage) because of:

(3a) domination by the strong-willed person

(3b) excessive devotion or misplaced loyalty

(3c) excessive desire to maintain harmony in the group

(4) The delusion may last from a few weeks to many years.

(5) The delusion is maintained despite the absence of objective data.


The shared delusion may involve a variety of conditions, such as parasitic infestation (delusional parasitosis). The group may visit many physicians or other health care providers.

Number of People Involved



folie a deux


folie a trois


folie a quatre


folie a cinq


folie a six


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