The objective of this study was to evaluate the efficacy and tolerability of extended release quetiapine fumarate (quetiapine XR) as maintenance monotherapy for patients with generalized anxiety disorder (GAD). Time-to-event (anxiety symptom recurrence; maximum 52 weeks) multicenter, randomized-withdrawal, parallel-group, double-blind, placebo-controlled study of quetiapine XR (50–300 mg/day) following open-label run-in (4–8 weeks) and open-label stabilization (≥12 weeks). Primary variable: time from randomization to anxiety event. Secondary variables included: Hamilton Anxiety Rating Scale (HAM-A) total, HAM-A psychic/somatic anxiety factors, Clinical Global Impression-Severity of Illness (CGI-S), and Quality of Life, Enjoyment and Satisfaction Questionnaire (Q-LES-Q) scores; adverse events (AE) reporting. Four hundred and thirty-two patients, stabilized on quetiapine XR, were randomized to continue quetiapine XR (N=216) or switch to placebo (N=216). Risk of anxiety symptom recurrence was significantly reduced by 81% for quetiapine XR versus placebo: hazard ratio=0.19 (95% confidence interval 0.12–0.31; P<0.001). Fewer patients receiving quetiapine XR (N=22, 10.2%) than placebo (N=84, 38.9%) experienced anxiety symptom recurrence. Significant differences were observed between quetiapine XR and placebo in: HAM-A total, psychic/somatic, CGI-S (all P<0.001) and Q-LES-Q (P<0.05) scores. AEs (>10%) during open-label treatment were dry mouth, sedation, somnolence, dizziness, fatigue, and constipation. During randomized treatment, the most common AEs for quetiapine XR were headache and nasopharyngitis. Quetiapine XR monotherapy reduced the risk of anxiety symptom recurrence in patients with GAD stabilized on quetiapine XR, with tolerability results consistent with the known profile of quetiapine.