Signs and symptoms of narcissistic personality disorder and the severity of symptoms vary. People with the disorder can:

• Have an exaggerated sense of self-importance
• Have a sense of entitlement and require constant, excessive admiration
• Expect to be recognized as superior even without achievements that warrant it
• Exaggerate achievements and talents
• Be preoccupied with fantasies about success, power, brilliance, beauty or the perfect mate
• Believe they are superior and can only associate with equally special people
• Monopolize conversations and belittle or look down on people they perceive as inferior
• Expect special favors and unquestioning compliance with their expectations
• Take advantage of others to get what they want
• Have an inability or unwillingness to recognize the needs and feelings of others
• Be envious of others and believe others envy them
• Behave in an arrogant or haughty manner, coming across as conceited, boastful and pretentious
• Insist on having the best of everything — for instance, the best car or office

At the same time, people with narcissistic personality disorder have trouble handling anything they perceive as criticism, and they can:

• Become impatient or angry when they don't receive special treatment
• Have significant interpersonal problems and easily feel slighted
• React with rage or contempt and try to belittle the other person to make themselves appear superior
• Have difficulty regulating emotions and behavior
• Experience major problems dealing with stress and adapting to change
• Feel depressed and moody because they fall short of perfection
• Have secret feelings of insecurity, shame, vulnerability and humiliation

It's not known what causes narcissistic personality disorder. As with personality development and with other mental health disorders, the cause of narcissistic personality disorder is likely complex. Narcissistic personality disorder may be linked to:

• Environment ― mismatches in parent-child relationships with either excessive adoration or excessive criticism that is poorly attuned to the child's experience
• Genetics ― inherited characteristics
• Neurobiology — the connection between the brain and behavior and thinking

Narcissistic personality disorder affects more males than females, and it often begins in the teens or early adulthood. Keep in mind that, although some children may show traits of narcissism, this may simply be typical of their age and doesn't mean they'll go on to develop narcissistic personality disorder.

Although the cause of narcissistic personality disorder isn't known, some researchers think that in biologically vulnerable children, parenting styles that are overprotective or neglectful may have an impact. Genetics and neurobiology also may play a role in development of narcissistic personality disorder.

Complications of narcissistic personality disorder, and other conditions that can occur along with it, can include:

• Relationship difficulties
• Problems at work or school
• Depression and anxiety
• Physical health problems
• Drug or alcohol misuse
• Suicidal thoughts or behavior