To investigate the relationship between cerebral leuko-araiosis and cognitive function in normal aged subjects, 48 neurologically normal aged volunteers (24 males, 24 females, 64-85 years old, mean age 75.2 years) with no silent lacunar lesions on their MRI images were examined. The severity of periventricular hyperintensity was estimated quantitatively based on the T1 values on MRI. Cognitive function was evaluated on the basis of P300 event-related potentials employing an auditory oddball paradigm. The severity of frontal lobe leuko-araiosis significantly increased with advancing age (p < 0.05), however, P300 latency was not correlated with age. There was no significant correlation between the severity of leuko-araiosis and P300 latency. The severity of leuko-araiosis was correlated with mean arterial blood pressure (p < 0.05). These results suggest that the severity of leuko-araiosis may be unrelated to cognitive function in normal aged subjects and that arterial blood pressure may contribute to the progression of leuko-araiosis.