Twenty-seven new cases of stroke in Down syndrome are reported, two probands, 13 patients from review of institutional records, and 12 patients from a survey of child neurologists. Forty-one patients from previous reports are summarized. Most stroke episodes were related to congenital heart disease and infections. Seven cases were associated with angiographic abnormalities; there were three cases of unknown etiology and four cases of moyamoya. The understanding of moyamoya and other causes of stroke may be advanced by further study of stroke in Down syndrome patients.