Although concepts of pathological narcissism are as old as psychology and psychiatry itself, only a small number of clinical studies are based on the criteria for narcissistic personality disorder (NPD), as defined in the Diagnostic and Statistical Manuals of Mental Disorders (DSM). As a result, NPD appears to be one of the most controversially discussed nosological entities in psychiatry. Whereas the majority of empirical studies used self or other ratings of NPD criteria to address issues of reliability and validity of the diagnostic category (i.e., internal consistency, factor structure, discriminant validity), only recent research has applied experimental designs to investigate specific features of NPD (e.g., self-esteem, empathy, shame). The aim of this review is to summarize available empirical data on NPD and relate these findings to current definitions of NPD (according to the DSM-5, [1]). In order to do so, this review follows the five steps to establishing diagnostic validity proposed by Robins and Guze [2], i.e., (1) clinical description, (2) laboratory studies, (3) delimitation from other disorders, (4) family studies, and (5) follow up studies. Finally, this review suggests pathways for future research that may assist further nosological evaluation of NPD and contribute to the overall goal, the improvement of treatment for patients.