['Voluntary attempts to suppress certain thoughts can paradoxically increase their intrusive return. Particular impairments in thought suppression are thought to be key mechanisms in the pathogenesis of mental disorders. To assess the role of this processing bias in the maintenance of generalized anxiety disorder (GAD), we investigated whether it is susceptible to cognitive-behavioural treatment (CBT).', '22 GAD patients and 22 healthy controls (HC) were tested twice within 15 weeks, with patients receiving CBT in between. A subset of patients was additionally tested while waiting for treatment to control for retest effects. Using a mental control paradigm, we measured intrusion frequency during the voluntary suppression of thoughts related to (a) the individual main worry topic, (b) a negative non-worry topic, and (c) a neutral topic. Self-reported worry was measured before and after treatment, and at 6-months follow-up.', 'Compared to HC, GAD showed specifically more worry-related intrusions. CBT reduced this bias to a healthy level, over and above mere test-retest effects.'] Does cognitive-behavioural therapy reduce unwanted thought intrusions in generalized anxiety disorder?