Cognitive behavioural therapy (CBT) is an empirically supported treatment for generalized anxiety disorder (GAD). Little is known about the effectiveness of CBT for GAD in real-world treatment settings.

This study investigated the effectiveness of group CBT and predictors of treatment response in an out-patient hospital clinic.

Participants (n = 386) with GAD participated in 12 sessions of group CBT at an out-patient clinic. Of those who provided at least partial data (n = 326), 84.5% completed treatment. Most questionnaires were completed at pre- and post-treatment; worry severity was assessed weekly.

Group CBT led to improvements in chronic worry (d = –0.91, n = 118), depressive symptoms (d = –1.22, n = 172), GAD symptom severity (d = –0.65, n = 171), intolerance of uncertainty (IU; d = –0.46, n = 174) and level of functional impairment (d = –0.35, n = 169). Greater pre-treatment GAD symptom severity (d = –0.17, n = 293), chronic worry (d = –0.20, n = 185), functional impairment (d = –0.12, n = 292), and number of comorbid diagnoses (d = –0.13, n = 299) predicted greater improvement in past week worry over treatment. Biological sex, age, depression symptom severity, number of treatment sessions attended, and IU did not predict change in past week worry over time.

These findings provide support for the effectiveness of group CBT for GAD and suggest the outcomes are robust and are either not impacted or are slightly positively impacted by several demographic and clinical factors.