Background: Borderline Personality Disorder (BPD) is a common mental disorder associated with raised mortality, morbidity and substantial economic costs. Although complex psychological interventions have been shown to be useful in the treatment of BPD, such treatments are expensive to deliver and therefore have limited availability and questionable cost-effectiveness. Less complex interventions are required for the management of BPD. A Joint Crisis Plan (JCP) is a record containing a service user's treatment preferences for the management of future crises and is created by the service user with the help of their treating mental health team. These plans have been shown to to be an effective way of reducing compulsory treatment in people with psychosis. However, to date they have not been used with individuals with BPD. This exploratory trial will examine whether use of a JCP is an effective and cost-effective intervention for people with BPD for reducing self-harm.Methods/Design: In this single blind exploratory randomized controlled trial, a total of 120 participants (age >18 years with a primary diagnosis of DSM-IV borderline personality disorder) will be recruited from community mental health teams and, after completing a baseline assessment, will be assigned to one of two conditions: (1) a Joint Crisis Plan, or (2) treatment as usual. Those allocated to the JCP condition will take part in a facilitated meeting, the purpose of which will be to agree the contents of the plan. Following the meeting, a typed version of the JCP will be sent to the patient and to any other individuals specified by the participant. All participants will be followed-up at 6 months. The primary outcome measures are: any self-harm event, time to first episode of self-harm and number of self-harm events over the follow-up period. Secondary outcome measures are length of time from contemplation to act of self-harm, help-seeking behaviour after self-harm, cost, working alliance, engagement with services and perceived coercion. Other outcome variables are quality of life, social impairment and satisfaction with treatment.Discussion: Results of this trial will help to clarify the potential beneficial effects of JCPs for people with BPD and provide information to design a definitive trial.