Dissociative Identity DisorderThis posttraumatic dissociative disorder was formerly known as Multiple Personality Disorder in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Test Revision (DSM- IV-TR). The DSM-V renamed it Dissociative Identity Disorder abbreviated to DID. “The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision describes dissociative identity disorder (DID) by means of two dissociative phenomena: a) amnesia (criterion C), and b) the presence of alter personalities (criteria A and B )” (Dell, 2002, p.10). Personality dissociation is the hallmark of the disorder. Dissociative identity disorder is characterized by “the adoption of several new identities (up to 100; the average is 15)” (Terwilliger, 2014). Each identity exhibits unique voices, postures, and behaviors. There are three important terms used when talking about identity. These are the alters, the host and the switch. “Alter – the different identities or personalities. Host – the identity that holds other identities together. Switch: rapid transformation from one personality to another” (Terwilliger, 2014). These identities were created as a natural defense mechanism that the body uses to protect itself from a traumatic experience by repressing its memories. History of Dissociative Identity Disorder Dissociative identity disorder was initially diagnosed as demonic possession. This diagnosis dates back to biblical times. "This article proposes a phenomenological model of therapeutic exorcism of demons for dissociative identity disorder, using the patient's perspective on perceived demons and empowering him to use his own spirituality to expel them," (Bull, 2001,.. .... half of the paper ......emergency visits with DID patients include flashbacks, self-mutilation, suicide attempts, and non-epileptic seizures. Some patients suffer from anxiety or panic disorders and other dissociative disorders. Conclusion Dissociative identity disorder is one of many dissociative disorders recognized by the DSM. It is differentiated by amnesia and the presence of different personalities. Over the years, many different diagnoses have been formulated. The first case dates back to biblical times along with several beliefs about causes and treatments. One of the best known cases is that of Sybil or Shirley Ardell Mason. This article has explored her case along with others to explain the disorder, history, causes, symptoms, prognosis, diagnosis. , the wrong diagnosis. , treatment and comorbidity of dissociative identity disorder.