A rare disorder in which a person holds a delusional belief that different people are in fact a single person who changes appearance or is in disguise. The syndrome may be related to a brain lesion and is often of a paranoid nature, with the delusional person believing themselves persecuted by the person they believe is in disguise. The condition is associated with schizophrenia, but can occur in isolation to other disorders. It is considered an extension of Capgras’ syndrome.

P. Courbon, G. Fail:
•  Syndrome d’illusion de Frégoli et schizophrénie.
   Bulletin de la Société clinique de médecine mentale, Pais, 1927, 15 : 121-125.

   Also in: Annals of Medical Psychology, 1927, 85: 289–290.

The authors decribed a 27 year old woman in London who believed she was being persecuted by two actors she often saw in the theatre. She believed these people pursued her closely, taking the form of people she knew or met.

•  Wikipedia.