Induced delusional disorder (also known as shared paranoid disorder or folie à deux) is an uncommon disturbance characterized by the presence of similar psychotic symptoms in two or more individuals. Most commonly a primary case can be distinguished from other one or more cases, in whom the symptoms are induced. the patients implied in the shared delusional symptoms are frequently linked by close relationship bonds, mostly family ties. Its epidemiology remains unclear, because very few data is available. There are some requirements concerning the persons involved for the development of this disorder:

1. 1. Close coexistence and intimate emotional links between the two people are observed;

2. 2. The delusional content is plausible and can be based on past events or expectations;

3. 3. Typically, the induced individual has an easily influenciable personality.

We describe and comment one case of shared paranoid disorder between a 29 year old schizophrenic patient and her 43 years old sister. both share a persecution and prejudice delusion involving the Chinese community of their hometown. after a few days of inward treatment at separated psychiatric wards, the delusional symptoms in the older sister started to improve.

Our intention is making a review on a diagnosis that remains controversial nowadays. Treatment should begin with the separation of the induced and the inducer. Anyhow, a psychopharmacological treatment is required in both individuals. It seems clear, however, that the prognosis of the induced and the inducer is different, according to a variety of factors.