In patients with schizophrenia, 'atypical' antipsychotics such as clozapine may be effective in the treatment of psychosis. In patients with borderline personality disorder (BPD), as far as the investigators know, no well designed controlled studies have been performed on the effect of one of the newer atypical antipsychotics on psychotic symptoms.

It is of interest to investigate the benefit of quetiapine treatment in these types of patients. Quetiapine possibly gives less side-effects because of the expected lack of elevated prolactin levels, which is of importance in this patient group, overrepresented by young females. In this double blind, randomized, placebo controlled, 8 week, parallel group, multi-center study, quetiapine (in flexible doses between 200 mg/day and 600 mg/day) will be compared with the placebo.

Inclusion Criteria:

• Patients with BPD according to Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition (DSM-IV)/Structured Clinical Interview for DSM-IV Axis II Personality Disorders (SCID-II) including criterion 9: transient, stress related paranoid ideation or severe dissociative symptoms.
• In- or outpatients

Exclusion Criteria:

• Depressive disorder
• Bipolar disorder
• Schizoaffective disorder/schizophrenia/delusional disorder/schizotypal personality disorder
• Alcohol- or substance dependence
• Quetiapine doses >100mg od use in the past

Somatic:

• History of trauma capitis
• Visual and auditive disorders
• Neurological disorders (epilepsy)
• Pregnancy
• No adequate contraception
• History of cardial complaints/cardiological disorder
• Known sensitivity for quetiapine