Changes in Symptom Severity, Schemas and Modes in Heterogeneous Psychiatric Patient Groups Following Short-term Schema Cognitive– Behavioural Group Therapy: A Naturalistic Pre-treatment and Post-treatment Design in an Outpatient Clinic M. F. van Vreeswijk, 1 * P. Spinhoven, 3,4 E. H. M. Eurelings-Bontekoe 3 and J. Broersen 1,2 1 G-kracht Psychomedisch Centrum, Delft, Amsterdam, The Netherlands 2 GGZ Delfland, Delft, The Netherlands 3 Department of Clinical and Health Psychology, Leiden University, Leiden, The Netherlands 4 Department of Psychiatry, Leiden University Medical Center, Leiden, The Netherlands Schema therapy has proven to be an effective treatment for patients with borderline personality disorder. However, little is known of its merits in other psychiatric (personality) disorders. Objective: This study investigated whether schema therapy in a group setting (group schema cognitive– behavioural therapy [SCBT-g]) was associated with changes in symptom and schema and mode severity. Furthermore, the aim was to search for baseline predictors and possible mediators of treatment outcome. Design and method: Sixty-three heterogeneous psychiatric outpatients who attended the SCBT-g were included as participants. In this naturalistic pre-treatment and post-treatment design, data were available on the Symptom Checklist 90, the Schema Questionnaire and the Young–Atkinson Mode Inventory. Results: All outcome measurements showed changes with moderate to high effect sizes, with 53.2% of the patients showing a significant reduction in severity of psychiatric symptoms and schemas and modes. Higher pre-treatment levels of the schema domain Other Directedness predicted greater symptom reduction. Pre-treatment to mid-treatment changes in schema severity predicted subsequent symptom improvement, but change in symptoms and schemas proved to be strongly correlated. Conclusions: In this naturalistic study, SCBT-g was associated with reduced symptom and schema and mode severity in more than half of the psychiatric outpatients. Furthermore, the results suggest that changes in schemas and symptomatology mutually reinforce each other. Copyright © 2012 John Wiley & Sons, Ltd. Key Practitioner Message: • Over 50% of ambulatory patients show clinical improvement after treatment in a short-term schema therapy group. • Other Directedness seems to be a predictor of schema group therapy success. • More randomized controlled trial studies and prediction and mediation studies on (short-term) schema group therapy are sorely needed. Keywords: Schema Therapy, Group Psychotherapy, Personality Problems, Outcome Study, Prediction, Mediation Schema therapy has proven to be both a clinically useful and cost-effective treatment for borderline personality disorder (BPD; van Asselt et al., 2008; Farrel, Shaw, & Webber, 2009; Giesen-Bloo et al., 2006; Nadort et al., 2009; Nordahl & Nysaeter, 2005), with a low dropout rate (Giesen-Bloo et al., 2006). However, despite the promising results of schema therapy for patients with BPD, little is known about its effectiveness for other psychiatric (personality) disorders, especially in group settings. *Correpondence to: Michiel van Vreeswijk, G-kracht Psychomedisch Centrum, 2611 KG Delft, Amsterdam, The Netherlands. E-mail: mf.vanvreeswijk@g-kracht.com Clinical Psychology and Psychotherapy Clin. Psychol. Psychother. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/cpp.1813 Copyright © 2012 John Wiley & Sons, Ltd.