Dissociative Identity Disorder, also known as DID, is one of the best-known mental disorders, made popular by fiction and films. Although controversial for years, Dissociative Identity Disorder has been accepted as a real disease by the medical profession for years. While the reality of the disease is far from what we often see in fiction, the truth is that cases of Dissociative Identity Disorder are diagnosed around the world all the time. Dissociative Identity Disorder is also known as "split personality" or "multiple personality" disorder.

Dissociative Identity Disorder refers to a mental disorder in which a person shows a series of completely different personalities, some of which are secondary and some which take over daily, at different times or during different situations. A person who is suffering from Dissociative Identity Disorder often retains his or her original identity, and adopts additional ones that come on and off into being depending on circumstance.

Diagnosing Dissociative Identity Disorder is extremely complex. Psychiatrists use specific guidelines when looking for signs of the disorder, including blackout periods, "lost time," and the presence of at least distinct identities that are unaware of each other's existence.

The multiple personality controversy has been around since the disease was first seriously studied in the mid-20th century. Many experts believe it is not a real disorder but a manifestation of other mental disturbances. Other experts argue that Dissociative Identity Disorder may be a way for the mind to hide past abuse or to trick itself into forgetting certain events. A diagnosis of "pure" Dissociative Identity Disorder remains rare.

A person who suffers from Dissociative Identity Disorder often changes personality during times of stress or difficult situations that his subconscious interprets she cannot handle. Multiple personalities tend to be absolutely different to each other, so, for example, a person who has a submissive personality in real life may have an alternate personality who is strong and stubborn, and another one who is bossy and domineering. It is also not uncommon for personalities to be of different ages, and the appearance of teen or child personalities in adults is commonplace.