Background: The psychological literature suggests that therapist perfectionism is common and potentially detrimental to client recovery. Little is known about the relationship between therapist perfectionism and client outcomes. Aims: This study aimed to measure perfectionism in High Intensity Cognitive Behavioural therapists, and establish any relationships between dimensions of therapist perfectionism, client outcomes and drop-out rates in treatment. Method: Thirty-six therapists took part in the study; levels of perfectionism were measured using a self-report questionnaire and these were analysed in relation to the clinical outcomes from a sample of their clients. Results: The results indicated that therapist perfectionism may be less common than previously suggested. Overall, a number of significant negative associations were observed between aspects of therapist perfectionism (e.g. having high standards for others), treatment efficacy and client retention in treatment. Conclusions: Therapist perfectionism is associated with CBT treatment outcomes; tentative recommendations for therapists managing their own schema as part of their clinical practice have been made, although further investigation is required.