The definition of clinical criteria for differential diagnosis of Vascular Dementia (VaD) and Alzheimer's disease (AD) remains controversial. A large group of patients selected was affected by chronic cerebrovascular disease classified as VaD or not (VND), according to DSM IV criteria. Neuropsychological performances of VaD patients were compared with a group of patients affected by probable AD, matched for age, education, and severity of disease. The comparison of performances did not reach statistical significance in single neuropsychological tasks. The results suggest that neuropsychological examination might not clearly differentiate between VaD and AD patients; the similar pattern of cognitive impairment is probably indicative of several common pathogenetic mechanisms.