Background: People with borderline personality disorder frequently experience crises. To date, no randomised controlled trials (RCTs) of crisis interventions for this population have been published. Aims: To examine the feasibility of recruiting and retaining adults with borderline personality disorder to a pilot RCT investigating the potential efficacy and cost-effectiveness of using a joint crisis plan. Method: An RCT of joint crisis plans for community-dwelling adults with borderline personality disorder (trial registration: ISRCTN12440268). The primary outcome measure was the occurrence of self-harming behaviour over the 6-month period following randomisation. Secondary outcomes included depression, anxiety, engagement and satisfaction with services, quality of life, well-being and cost-effectiveness. Results: In total, 88 adults out of the 133 referred were eligible and were randomised to receive a joint crisis plan in addition to treatment as usual (TAU; n = 46) or TAU alone (n = 42). This represented approximately 75% of our target sample size and follow-up data were collected on 73 (83.0%) participants. Intention-to-treat analysis revealed no significant differences in the proportion of participants who reported self-harming (odds ratio (OR) = 1.9, 95% CI 0.53-6.5, P = 0.33) or the frequency of self-harming behaviour (rate ratio (RR) = 0.74, 95% CI 0.34-1.63, P = 0.46) between the two groups at follow-up. No significant differences were observed between the two groups on any of the secondary outcome measures or costs. Conclusions: It is feasible to recruit and retain people with borderline personality disorder to a trial of joint crisis plans and the intervention appears to have high face validity with this population. However, we found no evidence of clinical efficacy in this feasibility study.