The aim of this prospective multicenter trial was to determine whether bypass surgery can prevent stroke recurrence in patients with major cerebral artery occlusive diseases and hemodynamic cerebral ischemia determined by quantitative measurement of cerebral blood flow, and whether improvement in hemodynamic cerebral ischemia by bypass surgery can prevent the progression of neuropsychological disorders or improve neuropsychological function. The subjects of this study were 196 patients who have been enrolled for 39 months from November 1, 1998 to January 30, 2002. Each patient underwent treatment according to the study program, and the 2-year follow-up survey of the patients is now under way. Of the 196 patients enrolled in the study, 98 each were assigned to the medically treated group and the surgically treated group. Fourteen patients in the medically treated group and 5 in the surgically treated group reached primary endpoint. The incidence of stroke recurrence in the surgically treated group was significantly lower than that in the medically treated group (p=0.046). The final results will become known in 2004.