Cryptogenic strokes are now thought to comprise about 25% of all ischemic strokes. These unable to find a precise mechanism of ischemia after standard workup, including transthoracic echocardiography, 12-lead electrocardiogram, inpatient cardiac telemetry monitoring, 24-hour Holter monitoring, magnetic resonance imaging, and a various vascular imaging of neck and brain arteries. Additional investigation identifies a likely mechanism in more than half these patients, such as cancer, aortic complicated lesion, coagulation disorders, etc. Most of cryptogenic strokes are cerebral embolism, arising from proximal arterial sources, heart, and/or venous sources. Patent foramen ovale (PFO) is found in up to half of young adults with cryptogenic stroke, and then percutaneous devices for closure of a PFO should be used for them after careful inspection.