Most therapists agree that the term "personality disorder" sounds awful, particularly to someone who hears it for the first time.  On the other hand, it does attempt to describe something that is very real for many people - that habitual ways of responding to life events can repeatedly cause difficulties in relationships, in work and in life in general.  When such problematic responses arise in many different areas of life to quite a severe degree, then "personality disorder" may be the most appropriate term to use.

Everyone has a personality, and one way of understanding what a personality is may be to think of it as our own collection of ways we tend to respond to things.  So for example, someone who has an optimistic, 'happy go lucky' personality may respond to news of a redundancy by shrugging their shoulders, thinking to themselves that "it'll turn out all right" and outwardly making a joke of it, whereas someone with an anxious, less trusting personality may respond to the same news by worrying a lot about it and trying to work out who 'had it in for them'.  How those two people will feel after the event, how long those feelings will last, and what they are likely to do in the following hours, days, weeks and months will probably be very different. 

"Personality disorder" is technically speaking a medical diagnosis.  The reason that it is in the list of diagnoses at all is because doctors have discovered over the years that a significant proportion of people repeatedly turn up for help suffering from emotional distress that seems to arise primarily from how they respond to events in their lives, and often these are responses that happen within relationships - relationships with partners, children, parents, colleagues and friends, and most significantly, their relationship with themselves.  The person consulting the doctor for help may or may not be suffering from a more obvious diagnosis at the time - such as depression, anxiety or eating disorder, for example - but an astute doctor who knows the person well enough will recognise that the underlying patterns of relationship the person has are likely to cause similar episodes of distress in the future as well. 

Hence the problem that is presented - the depression, anxiety or whatever - may be the most immediate problem but in order to tackle that episode fully and in order to prevent future distress it would be helpful to recognise the underlying personality patterns.  A diagnosis of personality disorder is a formal recognition of such underlying personality patterns, if they exist to such an extent that they are likely to cause significant repeated distress.

There are some common and unhelpful misconceptions about personality disorder.  It is not true that a diagnosis of personality disorder indicates that the entire personality is disordered, or 'wrong' in some way.  Everyone has aspects of their personality that get them into trouble from time to time, and none of us are perfect.  'Personality disorder' is therefore a matter of relative degree than one of fundamental difference.  Many people with personality disorder have aspects of great strength in their personality too - indeed, some have survived great trauma as children, and have come through in ways that many adults without such experiences would find it difficult to imagine. 

Another common misconception is that personality disorder is final, that is, no-one ever gets better from it.  Actually, the vast majority of people with personality disorder do recover from it, that is after a while no longer fulfill the diagnostic criteria for it.  "A while" though is usually measured in years rather than weeks or months.  This makes sense, as habits are nearly always difficult to change, and take time.  Sometimes it is difficult to notice the habits we have.  Psychological therapy can be helpful for people with personality disorder, helping to notice what the habits are, understanding where they may have come from, and, if needed, supporting people through the stages of taking risks by trying out different ways of responding.

www.personalitydisorder.org.uk

www.bbc.co.uk/health/conditions/mental_health/disorders_person.shtml