all information derived from entry 300.14 in the Diagnostic and Statistical Manual of Mental Disorders (Third Edition - Revised)

• The condition is defined by the presence of two or more distinct personalities in a single mind.
  
  
• Half of all cases involve more than 10 personalities.
  
  
• Personalities may have mental disorders of their own.
  
  
• Personalities may be aware of each other, and may even interact.
  
  
• Transitions between personalities is often quick, measured in seconds or minutes.
  
  
• Personality transition may be triggered by environment or hypnotic suggestion.
  
  
• Personality transition may follow a plan to which the personalities have agreed.
  
  
• Personalities may force transitions.
  
  
• Onset is most often in childhood.