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The ICD-10, the International Classification of Diseases, published by the World Health Organisation in Geneva  regards the Narcissistic Personality Disorder (NPD) as "a personality disorder that fits none of the specific rubrics". It relegates it to the category "Other Specific Personality Disorders" together with the eccentric, "haltlose", immature, passive-aggressive, and psychoneurotic personality disorders and types.
The American Psychiatric Association, based in Washington D.C., USA, publishes the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, Text Revision (DSM-IV-TR)  where it provides the diagnostic criteria for the Narcissistic Personality Disorder (301.81, p. 717).
The DSM-IV-TR defines Narcissistic Personality Disorder (NPD) as "an all-pervasive pattern of grandiosity (in fantasy or behaviour), need for admiration or adulation and lack of empathy, usually beginning by early adulthood and present in various contexts", such as family life and work.
The DSM specifies nine diagnostic criteria. Five (or more) of these criteria must be met for a diagnosis of Narcissistic Personality Disorder (NPD) to be rendered.
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Diagnostic criteria for 301.81 Narcissistic Personality Disorder (DSM IV - TR)
A pervasive pattern of grandiosity (in fantasy or behavior), need for admiration, and lack of empathy, beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following: