Symptoms of depersonalization during feared social situations are commonly experienced by individuals with social anxiety disorder (SAD). Despite its clinical relevance, it is not addressed in standard treatment manuals and it remains unclear if depersonalization is reduced by well-established treatments. This study investigated whether cognitive therapy (CT) for SAD effectively reduces depersonalization and whether pre-treatment severity of depersonalization predicts or mediates treatment outcome. In a randomized controlled trial, patients underwent the standardized Trier Social Stress Test before and after CT (n = 20) or a waitlist period (n = 20) and were compared to healthy controls (n = 21). Self-reported depersonalization was measured immediately after each stress test. Depersonalization significantly decreased following CT, especially in treatment responders (eta(2)(p) = 0.32). Pre-treatment depersonalization did neither predict nor mediate post-treatment severity of social anxiety. Further prospective studies are needed for a better scientific understanding of this effect. It should be scrutinized whether SAD-patients suffering from depersonalization would benefit from a more specific therapy. (C) 2016 Elsevier Ltd. All rights reserved.