What is a fregoli delusion?

Fregoli delusion, named after the Italian actor Leopoldo Fregoli, involves the erroneous belief that different people are actually the same person who is changing appearance or disguising his or her true identity. For example, the patient may mistakenly perceive the mail carrier every morning to be multiple doctors in disguise.

Common among schizophrenic patients, the term has become widely recognised in both medicine and popular culture with various examples occurring in media such as books, television and film.

The clinical notes for the syndrome were first detailed by Marc-Antoine Crocq in May 1927 but are often falsely credited to Courbon and Fail (1927 & 1928) whose publication on double subjective deliria and their clinical and forensic importance included similar ideas.