Waiting lists for psychotherapy for patients with personality disorders are increasing; there is an imbalance between the number of patients seeking help and the amount of therapy available. Thus, there is a need for time-limited treatments that are effective for specific patients and their specific problems. This pilot randomized controlled trial aimed to investigate the effectiveness of two 8-week group modules + treatment as usual (TAU): schema mindfulness-based cognitive therapy (SMBCT) and competitive memory therapy (COMET) with special attention to predictors and mediators of change. Patients (N = 58) were randomized to either SMBCT + TAU or COMET + TAU. The dropout rate was 34%. Time effects were found for both treatments, but neither was more effective than the other, and around 23% showed deterioration after treatment. Explorative analyses suggested that predictors for change were severity of psychological distress and a demanding and/or punitive attitude toward oneself at baseline. Global severity index change in the beginning of the treatment mediated schema changes later on in treatment. SMBCT + TAU and COMET + TAU might be mostly suitable for patients with high levels of symptom severity followed by high scores on parent modes. More research is needed to tailor these time-limited therapies to specific personality problems. (PsycInfo Database Record (c) 2020 APA, all rights reserved).