Stroke in trisomy 21 may be due to cardioembolism, atherosclerosis, vasculitis, 
moyamoya disease, sinus venous thrombosis, internal carotid hypoplasia or 
infections like endocarditis with septic emboli, meningitis or brain abscess. In 
rare cases, however, stroke etiology remains unexplained. We present a 19 year 
old Caucasian girl with trisomy 21 with a 47XX+21 karyotype who suffered at age 
11 years from a transient ischemic attack with left hemiparesis, and at age 
17 years from an ischemic stroke in the territory of the right cerebral medial 
artery. She suffered from arterial hypertension, obesity and 
hypercholesterolemia. Since blood coagulation studies, immunologic parameters, 
blood cultures, 24-h Holter monitoring, transthoracic and transesophageal 
echocardiography, magnetic resonance angiography of the extra- and intracranial 
vessels, thoracic and abdominal aorta and renal arteries did not provide any 
explanation for the stroke, implantation of a loop recorder is considered in 
order to detect episodes of clinically silent atrial fibrillation.