Objectives: Borderline personality disorder (BPD) is characterised by recurring crises, hospitalisations, self-harm, suicide attempts, addictions, episodes of depression, anxiety and aggression and lost productivity. The objective of this study is to determine the use of direct health care resources by persons with BPD in Ireland and the corresponding costs. 

Methods: This prevalence-based micro-costing study was undertaken on a sample of 196 individuals with BPD attending publicly funded mental health services in Ireland. All health care costs were assessed using a resource utilisation questionnaire completed by mental health practitioners. A probabilistic sensitivity analysis, using a Monte Carlo simulation, was performed to examine uncertainty. 

Results: Total direct healthcare cost per individual was €10 844 annually (ranging from 5228 to 20 609). Based on a prevalence of 1% and an adult population (18–65 years) of 2.87 million, we derived that there were 28 725 individuals with BPD in Ireland. Total yearly cost of illness was calculated to be up to €311.5 million. 

Conclusions: There is a dearth of data on health care resource use and costs of community mental health services in Ireland. The absence of this data is a considerable constraint to research and decision-making in the area of community mental health services. This paper contributes to the limited literature on resource use and costs in community mental health services in Ireland. The absence of productivity loss data (e.g. absenteeism and presenteeism), non-health care costs (e.g. addiction treatment), and indirect costs (e.g. informal care) from study participants is a limitation of this study.