NPD is a personality disorder in which the sufferer is extremely self-centered and is unable to empathise with or consider the feelings of those around them. They tend to be sensitive to criticism and like to receive admiration and adoration.
Symptoms include constant searching for approval and praise, self-absorption, self-importance, fragile self-esteem, exaggeration of talents, fantasies about power, unhealthy relationships, excessive jealousy of others, 'using' people to reach goals and an unrealistic or exaggerated self-image. Narcissism is speculated to be the root of antisocial personality disorder.
PREVALENCE AND SUSCEPTIBILITY
Those who had troubled childhoods tend to be most susceptible to personality disorders. It is estimated under 1% of the American population is undergoing treatment for NPD, though this doesn't reflect the true number of narcissists as they rarely seek treatment unless it increases their self worth or they are forced into it by court systems.
Treatment is generally not given for NPD, but therapy can be effective.
 - http://www.halycon.com/jmashmun/npd/
 - http://psychologytoday.com/conditions/histrionic.html
 - http://www.mayoclinic.com/health/narcissistic-personality-disorder/DS00652
 - http://www.narcissism.operationdoubles.com/prevalenceofnarcissism.htm
 - http://www.narcissism.operationdoubles.com/dignosticcriteria.htm