Narcissistic personality disorder (NPD), a term first used by Heinz Kohut in 1971, is a form of pathological narcissism acknowledged in the Diagnostic and Statistical Manual of Mental Disorders in 1980, in the edition known as DSM III-TR. Narcissistic personality disorder is characterized by extreme focus on oneself, and is a maladaptive, rigid, and persistent condition that may cause significant distress and functional impairment.

Diagnostic criteria
At least five of the following are necessary for a diagnosis (as with many DSM diagnoses, they must form a pervasive pattern; for example, a person who shows these criteria only in one or two relationships or situations would not properly be diagnosed with NPD):
has a grandiose sense of self-importance
is preoccupied with fantasies of unlimited success, power, brilliance, beauty, or ideal love
believes that he or she is "special" and unique and can only be understood by other special people
requires excessive admiration
strong sense of entitlement
takes advantage of others to achieve his or her own ends
lacks empathy
is often envious or believes others are envious of him or her
arrogant affect.

Info Source, Links and more info:
http://en.wikipedia.org/wiki/Narciss...ality_disorder