Neuropsychological studies of 50 patients with Lewy body dementia (LBD) and 50 patients with Alzheimer's disease (AD) were performed to assess the characteristics of the cognitive impairments in these diseases. In patients with dementias of similar severities, patients with LBD showed greater impairment of executive and visuospatial functions and had more marked neurodynamic dysfunction. Patients with AD showed more profound memory disorders.