Background and Objectives: Dialectical behaviour therapy (DBT) trains participants to use behavioural skills for managing their emotions. The study aimed to evaluate whether skills use is associated with positive treatment outcomes independently of treatment processes that are common across different therapeutic models. Method: Use of the DBT skills and three common treatment processes (therapeutic alliance, treatment credibility and self-efficacy) were assessed every 2 months for a year in 70 individuals with borderline personality disorder receiving DBT. Mixed-multilevel modelling was used to determine the association of these factors with frequency of self-harm and with treatment dropout. Results: Participants who used the skills less often at any timepoint were more likely to drop out of DBT in the subsequent two months, independently of their self-efficacy, therapeutic alliance or perceived treatment credibility. More frequent use of the DBT skills and higher self-efficacy were each independently associated with less frequent concurrent self-harm. Treatment credibility and the alliance were not independently associated with self-harm or treatment dropout. Limitations: The skills use measure could not be applied to a control group who did not receive DBT. The sample size was insufficient for structural equation modelling. Conclusion: Practising the DBT skills and building an increased sense of self-efficacy may be important and partially independent treatment processes in dialectical behaviour therapy. However, the direction of the association between these variables and self-harm requires further evaluation. (C) 2016 Elsevier Ltd. All rights reserved.