Recent reports showing the favorable role of patent foramen ovale (PFO) closure in patients with cryptogenic stroke have raised the issue of selecting optimal candidates. This study, DEFENSE-PFO (Device Closure Versus Medical Therapy for Cryptogenic Stroke Patients With High-Risk Patent Foramen Ovale), evaluated whether the benefits of PFO closure can be determined on the basis of the morphologic characteristics of the PFO, as evaluated by transesophageal echocardiography. Patients with cryptogenic stroke and high-risk PFO were divided between a transcatheter PFO closure and a medication-only group. High-risk PFO included PFO with atrial septal aneurysm, hypermobility (phasic septal excursion into either atrium ≥10 mm), or PFO size (maximum separation of the septum primum from the secundum) ≥2 mm. The primary endpoint was a composite of stroke, vascular death, or Thrombolysis In Myocardial Infarction-defined major bleeding during 2 years of follow-up. From September 2011 until October 2017, 120 patients (mean age: 51.8 years) underwent randomization. PFO size, frequency of septal aneurysm (13.3% vs. 8.3%; p = 0.56), and hypermobility (45.0% vs. 46.7%; p > 0.99) were similar between the groups. All PFO closures were successful. The primary endpoint occurred exclusively in the medication-only group (6 of 60 patients; 2-year event rate: 12.9% log-rank p = 0.013; 2-year rate of ischemic stroke: 10.5% p = 0.023). The events in the medication-only group included ischemic stroke (n = 5), cerebral hemorrhage (n = 1), Thrombolysis In Myocardial Infarction-defined major bleeding (n = 2), and transient ischemic attack (n = 1). Nonfatal procedural complications included development of atrial fibrillation (n = 2), pericardial effusion (n = 1), and pseudoaneurysm (n = 1). PFO closure in patients with high-risk PFO characteristics resulted in a lower rate of the primary endpoint as well as stroke recurrence. (Device Closure Versus Medical Therapy for Cryptogenic Stroke Patients With High-Risk Patent Foramen Ovale DEFENSE-PFO; NCT01550588).