Electroencephalogram　(EEG)　activity,　recorded　while　performing　an　＂odd　ball＂　detection　task,　was　compared　between　patients　with　early　vascular　dementia　(VD),　healthy　young　controls　and　healthy　elderly　controls　performing　the　same　task.　The　data　were　analyzed　using　the　event-related　synchronization/desynchronization　(ERS/ERD)　method.　VD　patients,　compared　with　controls,　showed　decreased　ERS　effects　in　the　delta　frequency　band　(0.5-3.5Hz)　of　EEG　after　the　target　stimulus　appeared　in　frontal,　central　and　parietal　regions.　Similarly,　elderly　controls　also　showed　a　decreased　ERS　compared　with　young　controls　only　in　central　and　parietal　regions.　As　part　of　this　analysis,　we　introduce　a　novel　quantitative　index,　the　Event-related　Energy　Change　Progression　(EECP),　which　provides　a　reliable　measure　that　distinguishes　these　groups　and　thereby　provides　a　promising　marker　for　early　diagnosis　of　VD.