Differential diagnosis of Alzheimer's disease (AD) and vascular dementia(VaD) has an important bearing on the diagnosis and management of patients with dementia. This article provides a guideline for the differential diagnosis through 1) history taking, 2) neurological examination, 3) neuropsychological tests, and 4) neuroimaging studies. VaD consists of etiologically and clinically heterogeneous subtypes that include multi-infarct dementia (MID), single strategic infarct dementia, and subcortical vascular dementia. Patients with MID and single infarct dementia con be easily differentiated from patients with AD. However, clinical manifestations of subcortical vascular dementia can mimic those of AD, which may lead primary physicians to misdiagnose subcortical vascular dementia as AD. The issue of differential diagnosis is further complicated by the fact that many patients may have AD with concomitant VaD (mixed dementia).