Cerebral atrophy and regional cerebral blood flow (CBF) were examined in 52 chronic stroke patients with dementia, pre-dementia or non-dementia (according to the Dementia Scale). The index of cerebral atrophy was estimated on computed tomography, and CBF was determined using 133Xe inhalation method. Cerebral atrophy indices were not significantly different among various degrees of dementia except a slightly increased cella media index in pre-dementia group. Average values for CBF were bilaterally reduced in dementia, being 28.5 +/- 4.4 for affected hemisphere and 31.0 +/- 3.2 ml/100g/min for non-affected one. Compared with those, CBF were higher in pre-dementia (37.3 +/- 8.7 and 39.4 +/- 8.2 ml/100 g/min, p less than 0.05 vs dementia, respectively) and more higher in non-dementia (45.8 +/- 10.2 and 48.5 +/- 10.4 ml/100 g/min, p less than 0.01 vs pre-dementia, respectively). Of 11 recurrent stroke patients, 5 with newly developed dementia after the second attack presented the preceding CBF reduction 10 to 34 months prior to the recurrence. Present results suggest that bilateral reduction of CBF may be the primarily important factor for the initiation or development of vascular dementia, and the CBF reduction seems to precede the symptom of dementia.