The chief symptom of dissociative identity disorder (DID) is the presence of multiple personalities, each of which controls the patient’s behavior at one time. Typically a patient’s primary identity has the person’s own given name and is passive, dependent, guilty and depressed. Meanwhile, other personalities - or alters - that surface at different times are more likely to be hostile, controlling and self-destructive.

The symptoms of DID include behavioral changes in the patient. These changes depend on which personality is in control. For example, the person may appear quiet or boisterous, male or female, or even right-handed or left-handed depending on the personality that is in control. In some patients, alters may have a different vocabulary, possess different general knowledge, have allergies or need eye glasses.

Patients who are under the control of one alter may not remember events that occurred when another alter was in control. Some alters may be aggressive toward certain people or toward other alters. People may exhibit up to 100 or more different identities. However, about half of all patients experience 10 or fewer personalities.

People with DID often experience episodes of amnesia or time loss. They may be greeted by people they do not remember meeting or find possessions they do not recall purchasing. Patients with DID may also suffer from depression or thoughts of suicide. Self-injury is commonplace among patients with DID and many patients have abused psychoactive substances at some time. About one-third of patients with DID may experience auditory or visual hallucinations, according to the National Alliance on Mental Illness (NAMI).