A delusion is a fixed false belief based on an inaccurate interpretation of an external reality despite evidence to the contrary. The belief is not congruent with one’s culture or subculture, and almost everyone else knows it to be false.

The diagnosis of a delusional disorder occurs when a person has one or more non-bizarre (situations that can take place in real life, although not real but are possible) delusional thought for one month or more, that has no explanation by another physiological, substance-induced, medical condition or any other mental health condition. An individual’s cultural beliefs merit consideration before coming to the diagnosis. Cultural beliefs also impact the content of delusions.