After Alzheimer's disease (AD), vascular dementia (VaD) is the most common cause of dementia among the elderly. Abnormalities in neurotransmitter pathways are common pathogenic mechanisms shared by AD and VaD. For one month we studied the effects of donepezil, an acetylcholinesterase inhibitor (5 mg daily), on the cognitive system using P300 auditory event-related potentials (P300) and neuropsychological tests in 10 patients affected by probable VaD according to the NINDS-AIREN criteria. Our data showed a significant improvement of neuropsychological items and P300 latency after one month of donepezil treatment. In conclusion both P300 and neuropsychological tests are indicated in patients with VaD to confirm the efficacy of donepezil treatment during follow-up.