IMPORTANCE Pulmonary vein isolation (PVI) is a recommended treatment for patients with atrial fibrillation, but it is unclear whether it results in a lower risk of stroke. OBJECTIVES To investigate the proportion of patients discontinuing anticoagulation treatment after PVI in association with the CHA(2)DS(2)-VASc (congestive heart failure, hypertension, age amp;gt;= 75 years [doubled], diabetes, stroke [doubled], vascular disease, age 65-74 years, sex category [female]) score, identify factors predicting stroke after PVI, and explore the risk of cardiovascular events after PVI in patients with and without guideline-recommended anticoagulation treatment. DESIGN, SETTING, AND PARTICIPANTS A retrospective cohort studywas conducted using Swedish national health registries from January 1, 2006, to December 31, 2012, with a mean-follow up of 2.6 years. A total of 1585 patients with atrial fibrillation undergoing PVI from the Swedish Catheter Ablation Register were included, with information about exposure to warfarin in the national quality register Auricula. Data analysis was performed from January 1, 2015, to April 30, 2016. EXPOSURES Warfarin treatment. MAIN OUTCOMES AND MEASURES Ischemic stroke, intracranial hemorrhage, and death. RESULTS In this cohort of 1585 patients, 73.0% were male, the mean (SD) age was 59.0 (9.4) years, and the mean (SD) CHA(2)DS(2)-VASc score was 1.5 (1.4). Of the 1585 patients, 1175 were followed up for more than 1 year after PVI. Of these, 360 (30.6%) discontinued warfarin treatment during the first year. In patients with a CHA(2)DS(2)-VASc score of 2 or more, patients discontinuing warfarin treatment had a higher rate of ischemic stroke (5 events in 312 years at risk [1.6% per year]) compared with those continuing warfarin treatment (4 events in 1192 years at risk [0.3% per year]) (P = .046). Patients with a CHA(2)DS(2)-VASc score of 2 or more or those who had previously experienced an ischemic stroke displayed a higher risk of stroke if warfarin treatment was discontinued (hazard ratio, 4.6; 95% CI, 1.2-17.2; P = .02 and hazard ratio, 13.7; 95% CI, 2.0-91.9; P = .007, respectively). CONCLUSIONS AND RELEVANCE These findings indicate that discontinuation ofwarfarin treatment after PVI is not safe in high-risk patients, especially those who have previously experienced an ischemic stroke.