The current study examined the phenomenon of sudden gains (i.e., rapid symptom reductions between two treatment sessions) in individuals who received cognitive-behavioral treatment for generalized anxiety disorder (GAD). The sample consisted of 59 Francophone adults with a primary diagnosis of GAD who completed a 14-week evidence-based treatment. Throughout treatment, participants completed the Penn State Worry Questionnaire—Past Week on a weekly basis. They also received assessments of GAD symptoms at intake and treatment termination using the Anxiety Disorders Interview Schedule for DSM-IV, the Worry and Anxiety Questionnaire (WAQ), and the Penn State Worry Questionnaire (PSWQ). Clients who experienced at least one sudden gain (20.34 % of the sample) experienced greater symptom reductions from pre-to post-treatment on the WAQ and the PSWQ than clients who did not experience a sudden gain. Our results suggest that the experience of sudden gains predicts positive treatment outcomes during cognitive-behavioral treatment for GAD.