Personality Disorders

A personality disorder is a type of mental disorder in which you have an unhealthy pattern of thinking, functioning and behaving, an enduring set of thoughts feeling and behaviours, present since before adolescence and persistent throughout adult life.

No single cause exists for personality disorder. The influence of genetic factors is evidenced by research but this evidence is balanced by evidence of the frequency and force of a childhood history of environmental disadvantage, trauma, neglect and loss. 

There are many types of personality disorders, however three broad groups or clusters of personality disorder are generally described by mental health definitions. These diagnostic groups are Cluster A (Odd or Eccentric), Cluster B (Dramatic or Histrionic) and Cluster C (Anxious or Dependent).  

Common features described in Cluster B disorder, known as borderline personality disorder, or more recently known as emotionally unstable personality disorder (EUPD), include a tendency of:

  • Impulsivity
  • Difficulty controlling emotions
  • Feeling bad about yourself
  • Repeated self-harm
  • Feeling ‘empty’
  • Rapidly forming relationships and just as rapidly losing them
  • Feelings of persecution  
  • And when stressed, a tendency to hear noises or even voices.

The number of people with EUPD and even the number of people who receive this diagnosis is not clear. 

When you put all the personality disorders together, studies estimate prevalence between one in 20 of the population and one in five of the population depending on the criteria in the literature. For EUPD it is estimated (in the USA) that somewhere in the region of 1.5% of the population have this condition.

More information

Visit our Frequently Asked Questions for more information on mental health and the services we offer.

  • Treatment

    Personality disorders can be successfully managed

    Different treatment settings and treatment plans may be effective for different people depending on the type of disorder, age, severity of symptoms, underlying causes and support networks available to the individual.  

    At St Patrick’s Mental Health Services, we offer inpatient and outpatient and day patient care. Two of our day programmes for personality disorder include Dialectical Behavioural Therapy and Radical Openness.


  • Useful resources


    • Depression – The Commonsense Approach – Tony Bates
    • Mind Over Mood – Greenberger/Padeskey
    • Overcoming Depression – Paul Gilbert
    • Depression – Your Questions Answered – Melvyn Lurie

    Check the Information Centre Book Shop for availability and a wider selection of books.

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Schizophrenia & Psychosis


For general queries, please call us. For more on mental health and our services, see our frequently asked questions (FAQs).

01 249 3200 See our FAQs


Contact Referral and Assessment Service for queries regarding referrals to our services.

01 249 3635 See more from our referrals team