The first documented case of what was probably DID is from 1584. Jeanne Fery had multiple personalities with their own names, personality traits and body language. They had similar roles that are typical of DID - toddler, self-helper, protector and internal perpetrator. She heard them inside her head and they could take over her body. She also had eating disorders, self-harm problems and conversion syndrome/somatoform syndrome. As a child she had been subjected to physical abuse and probably also sexual abuse. All of this is documented in the exorcisms she underwent. So it was seen as a spiritual possession.

There is a similar case from 1623. Sister Benedetta was a nun who was "possessed" by three angel boys. The three boys had different voices, dialects and facial expressions. Sister Benedetta had amnesia and, like Jeanne, also had eating disorders and self-harm problems. She also had problems with chronic pain. Her parents had shown signs that they also possibly had dissociative disorders. Her father died when she was 9 years old and Benedetta's symptoms became "uncontrollable" and she was put in a convent. One of the angel boys was fixed at the age of 9.

The first person believed to have been diagnosed was Louis Auguste Vivet in 1882. It is unclear whether the diagnosis was "hysteria" or what was called "double personality disorder", both seem to be mentioned in medical records. Louis was abused as a child and had what were called "hysterical attacks" where he then changed personalities and experienced amnesia. At the age of 17, he was hospitalized for a long time when he lost feeling in his legs after a snakebite. After a month in the hospital, he had an attack that is said to have lasted 50 hours, and after that he did not remember any of the doctors or fellow patients from the previous month. 10 different personalities were identified in him over the next few years.

However, there are differing opinions among professionals today about how many sub-persons he had, or if he even had any. None of these cases can be proven and there will always be differing opinions about them.
Spiritual possession was long used as an explanation for the symptoms and the "treatment" was then exorcism.

During the late 18th century and early 19th century, medical terms such as "exchanged personalities" and "double personality disorder" began to appear. Towards the end of the 19th century, "hysteria" appeared in slightly different variations. All of these seem to have been used during the late 19th century.

Louis Auguste Vivet, who was mentioned earlier as the first to be diagnosed (1882), was referred to in early medical records as having "double personalities". Sometimes it was written that there were exactly two sub-personalities, but some records show that there were more. It is suspected that the doctors tried to keep it down to only two sub-personalities in the medical record so that he would fit into that particular diagnosis. The same thing is documented from other cases from this time. Later it was changed to having "hysteria" and then more sub-personalities began to be recorded.

Dr. Jean Martin Charcot is considered by some to be the discoverer of DID in the 1880s. He called it "hystero-epilepsy". Research into dissociation can be said to have begun with Pierre Janet's (1889) description of the fact that trauma seems to be a prerequisite for dissociation. James, Charcot, Breuer, Freud and Jung also wrote about dissociation. In 1896, Freud presented his theory of seduction. The idea that hysterical patients had been exposed to sexual trauma in childhood was far too strong for Freud's time and he was ridiculed. Freud later abandoned his initial theory that trauma and sexual abuse in childhood were the cause of hysteria in favor of the child wanting to have sexual contact with his parents. According to this view, the child's memory fragments are also wishful fantasies.

However, Pierre Janet maintained his position that his patients who showed hysterical symptoms had been exposed to trauma and abuse in childhood. Janet also developed his theory that traumatization is due to our inability to handle a situation with overwhelming threat and danger. We become helpless and develop a state of such intense fear that our feelings cannot be stored in memory. The traumatizing experience does not disappear, but lives on as an unconscious fixation in our consciousness where it continues to influence our lives and our actions. It then becomes difficult to organize and structure consciousness. This thinking has been refined by Onno van der Hart (1989 onwards), among others, and now forms the basis for parts of the theory of structural dissociation.

In 1918, the term "hysterical psychoneurosis" was coined, which was later used in the first DSM manual in 1952. Unfortunately, we cannot find what the exact name in Swedish was. In Sweden, we use the ICD as a diagnostic manual instead of the DSM. We have not found anything about the earlier terms in the ICD as our sources are from countries that use the DSM.

In 1968, DSM-II came out and the name was changed to multiple personality disorder. In 1994, the name was changed to dissociative identity disorder when DSM-IV was released. But the name multiple personality disorder unfortunately sticks around for a while, especially in film and television, and even in things produced long after the name change. Many still believe that is the name of the diagnosis. And many confuse it with schizophrenia.

Between 1880 and 1920, DID, under various "hysteria"-related names, was something that was diagnosed and discussed quite a lot in healthcare. You could say it was a popular diagnosis.

Around 1910, schizophrenia was introduced as a term (after previously being called "dementia praecox"). By 1927, schizophrenia had increased drastically as a diagnosis, while DID/"hysterical psychoneurosis" had decreased at the same rate. Schizophrenia was now a popular diagnosis, and DID was not. The number of people who actually had each illness did not change, of course, but both before and after that shift, a lot of people were certainly misdiagnosed.
The original description of schizophrenia included multiple personalities as a symptom. But even after the multiple personalities part was removed from the description, the two continued to be confused. This may have something to do with the earlier description, but also with the fact that the word schizophrenia translates to split mind in English. What was meant by the name was not split as in multiple personalities, but a split between logic and emotions.

According to a survey by the National Alliance on Mental Illness, 64% of the US population believes that schizophrenia includes multiple personalities.
From a healthcare perspective, there may be similarities in the conditions that pose a risk of misdiagnosis, for example, that in both cases voices can be heard. Schizophrenia was for a long time (and perhaps still is) the "more popular" of them and is perhaps therefore more accessible/top of mind for healthcare professionals to go to when they have been told that a patient hears voices. Today, however, many healthcare providers know that how the voices are heard, i.e. whether they come from inside or outside the head, what they say and how the patient perceives them, plays a role in whether it is a psychotic illness or a dissociative disorder.