Objectives. The study aims at evaluating the suitability of applying the transtheoretical model (TTM) stage-of-change construct to the treatment with dialectical behaviour therapy (DBT) of borderline personality disorder (BPD). Design. Stages of change were assessed by means of the University of Rhode Island Change Assessment (URICA) scale prior to and after 3 months DBT skills group psychotherapy. Method. The sample was comprised of 79 people with BPD (86% of females) at pretreatment, and 42 patients (80% of females) at post-treatment. All patients were referred from clinical services and diagnosed by means of two semi-structured interviews. Results. In pre-treatment assessment, precontemplation scores correlated significantly and negatively with the other subscales (contemplation, action, and maintenance) and these three subscales also correlated significantly and positively with each other. The precontemplation stage was directly related to drop-out from the DBT group. The action subscale and the committed action (CA) composite score were significantly higher by the end of the DBT group treatment. However, with the absence of a control group it cannot be assured that these increases were directly related to DBT intervention. Conclusions. In this observational design the stages of change of TTM seemed applicable to the DBT conceptualization of BPD and could further our understanding of the process of change in people with BPD treated with DBT. © 2008 The British Psychological Society.