Background: Up to one in five women meet diagnostic criteria for an anxiety disorder during the perinatal period (i.e. pregnancy and up to 1 year postpartum). While psychotropic medications are effective, they are associated with risks for mothers and babies. There is a growing demand for evidence-based non-pharmacological treatments for perinatal anxiety. Objective: To evaluate the effectiveness of a cognitive behavioral group therapy protocol for perinatal anxiety. Methods: In total, 96 women were randomized to cognitive behavioral group therapy or waitlist at a clinic specializing in women’s mental health. Participants were 22–41 years of age, pregnant or up to 6 months postpartum and had an anxiety disorder with or without comorbid depression. Results: Compared to waitlist, participants in cognitive behavioral group therapy reported significantly greater reductions in the primary outcome of anxiety (State-Trait Inventory of Cognitive and Somatic Anxiety, η2p = .19; Hamilton Anxiety Rating Scale, η2p = .16), as well as in secondary outcomes including worry (Penn State Worry Questionnaire, η2p = .29), perceived stress (Perceived Stress Scale, η2p = .33) and depressive symptoms (Edinburgh Postnatal Depression Scale, η2p = .27; Montgomery–Åsberg Depression Rating Scale, η2p = .11). Maternal status (pregnant, postpartum) and medication use were unrelated to treatment outcomes. All gains were maintained, or continued to improve, at 3-month follow-up. Conclusion: Cognitive behavioral group therapy was effective in improving anxiety and related symptoms among women with anxiety disorders in the perinatal period.