Folie à deux

The article presents some old and modern concepts of folie à deux, as well as the epidemiology, etiology, prognosis and course of this disorder. The basic principles of diagnosis and treatment, and some therapeutic dilemmas are outlined. The author calls attention to a nosologic connection of this disorder with reactive psychosis, pointing out that further research of folie à deux will notably improve our knowledge of the etiology of delusions in general.