The aim of the study was to investigate if the addition of cognitive behavioural therapy to treatment as usual (CBT plus TAU) in participants with borderline personality disorder would decrease the number of participants with emergency (i.e. unplanned) psychiatric or accident and emergency room contact or episode of deliberate self-harm over twelve months treatment and twelve months follow-up, compared with treatment as usual (TAU). The study also examined whether CBT plus TAU would lead to superior improvement in quality of life, social, cognitive and mental health functioning than TAU alone.

The trial is being carried out in three centres in the UK: Glasgow, London and Ayrshire (Ayrshire and Arran). Treatment as Usual (TAU) therefore reflected what is likely to be available in the UK.

Patients were eligible if they satisfied the following criteria:

1. Aged between 18 and 65.
2. Met criteria for at least 5 items of the borderline personality disorder using the Structured Clinical Interview for DSM IV Axis II Personality Disorders (SCID -II)(First, Gibbon, Spitzer, Williams & Benjamin, 1997)
3. Had received either in-patient psychiatric services or an assessment at Accident and Emergency services or an episode of deliberate self-harm (either suicidal act or self-mutilation) in the previous 12 months.
4. Able to give informed consent.

Exclusion criteria were as follows:

1. Currently receiving in-patient treatment for a mental state disorder,
2. Currently receiving a systematic psychological therapy or specialist service, particularly psychodynamic psychotherapy,
3. Insufficient knowledge of English to enable them to be assessed adequately and to understand the treatment approach,
4. Temporarily resident in the area,
5. The existence of an organic illness, mental impairment, alcohol or drug dependence, schizophrenia or bipolar affective disorder, as assessed by SCID I,/P (W/ Psychotic Screen)(version 2) (First, Spitzer, Gibbon, Williams, 1996).

Inclusion Criteria:

1. Aged between 18 and 65.
2. Met criteria for at least 5 items of the borderline personality disorder using the Structured Clinical Interview for DSM IV Axis II Personality Disorders (SCID -II)(First, Gibbon, Spitzer, Williams & Benjamin, 1997)
3. Had received either in-patient psychiatric services or an assessment at Accident and Emergency services or an episode of deliberate self-harm (either suicidal act or self-mutilation) in the previous 12 months.
4. Able to give informed consent.

Exclusion Criteria:

1. Currently receiving in-patient treatment for a mental state disorder,
2. Currently receiving a systematic psychological therapy or specialist service, particularly psychodynamic psychotherapy,
3. Insufficient knowledge of English to enable them to be assessed adequately and to understand the treatment approach,
4. Temporarily resident in the area,
5. The existence of an organic illness, mental impairment, alcohol or drug dependence, schizophrenia or bipolar affective disorder, as assessed by SCID I,/P (W/ Psychotic Screen)(version 2) (First, Spitzer, Gibbon, Williams, 1996).