How rare is it to have multiple personalities?

Answer 1

So rare that a large number of psychiatrists and psychologists doubt it even exists and is a misdiagnosis of something else.

Answer 2

Dissociative Identity Disorder (formerly known as Multiple Personality Disorder) is a rare condition, with a prevalence thought to be less than 1% of the general population. It is often associated with a history of severe childhood trauma or abuse. Treatment typically involves therapy to integrate the different personalities into a cohesive sense of self.