The actual cause of Dissociative Identity Disorder is not fully known. There are, however, many theories that psychologists have on what the causes may be. The cause is believed to be childhood trauma, mainly physical and sexual abuse. Studies have shown that there is some type of documentation of abuse in about 95% of young patients with Dissociative Identity Disorder (Kluft, 2003). This is usually the case because of the stage of the development that children are at when they experience the trauma. The first alter usually develop is around 6 years of age (Dissociative identity disorder (formerly multiple personality disorder), n.d.). The ability to dissociate becomes a defense mechanism for these children.  These alters usually don't come out until much later in life. When the person is in a situation that is too overwhelming the alters usually come out because this is the only way these people known how to cope.

Childhood abuse is not believed to be the only cause of Dissociative Identity Disorder. It appears that there also may be a biological link when it comes to DID. Many people who have Dissociative Identity Disorder have a family history of mental illness. This is most often either some type of dissociative disorder or schizophrenia. People who have a family history of mental illness may be more prone to develop Dissociative Identity Disorder but may not actually develop the disorder unless they experience some type of childhood trauma. People who are easily hypnotized are also believed to be more prone to develop Dissociative Identity Disorder. This may be due to the fact that they dissociate more easily and this becomes an easy method for people to cope with stressful situations.