This article evaluates a pilot mentalization-based treatment programme for borderline personality disorder (BPD), which had an art therapy group as one of its three components. Evaluation involved a range of standardised measures and showed the programme had positive results with increases in distress tolerance, lowered service use and at least two participants no longer meeting criteria for the BPD diagnosis. The question was asked about what art therapy might contribute to mentalization in this context. A qualitative research strategy was undertaken to explore one of the author’s experience of art therapy as one of the programme’s service users. Repeated rounds of audio-recorded interviews resulted in eight themes which describe what helped and what should be avoided in art therapy treatment of BPD. The service user view was that art therapy was an essential ingredient in helping to develop greater mentalization. The study suggests that in anchoring mental content in an externalised form, art therapy offers the flexibility to slow down the process of explicit mentalization to a manageable pace. These findings were linked with similar service user research in Norway and the USA