Purpose - Previous research indicates that mentalisation-based treatment (MBT) is an effective therapeutic programme for difficulties associated with borderline personality disorder (BPD). The purpose of this paper is to explore service user experiences of the therapy. Design/methodology/approach -Seven adults (five female and two male), recruited via three NHS trusts, were interviewed. Participants were attending intensive out-patient MBT for BPD between 3 and 14 months. Data were analysed using interpretative phenomenological analysis. Findings -Participants experienced the group component of MBT as challenging and unpredictable. They highlighted developing trust as key to benefitting from MBT. This was much more difficult to achieve in group sessions than in individual therapy, particularly for those attending MBT for less than five or six months. The structure of MBT generally worked well for participants but they identified individual therapy as the core component in achieving change. All participants learned to view the world more positively due to MBT. Practical implications -Enhanced mentalisation capacity may help address specific challenges associated with BPD, namely, impulsivity and interpersonal difficulties. MBT therapists are confronted with the ongoing task of creating a balance between sufficient safety and adequate challenge during MBT. Potential benefits and drawbacks of differing structural arrangements of MBT programmes within the UK are considered. Originality/value -Learning about service user perspectives has facilitated an enhanced understanding of experiences of change during MBT in addition to specific factors that may impact mentalisation capacity throughout the programme. These factors, in addition to implications for MBT and suggestions for future research, are discussed.