Vascular dementia is most often the result of multiple lesions affecting deep brain structures and the white matter. Diagnosis sometimes appears much simpler than it really is. Indeed, it is difficult to evaluate the impairment of higher brain functions and even to affirm dementia. Although the definition of dementia is simple theoretically, in clinical practice it is sometimes particularly difficult to assess when neurological impairments cause a socio-professional handicap. Two pitfalls should be avoided. First, a patient with signs of mental deficiency and a vascular lesion of brain vessels so easily identified by CT scan or MRI does not necessarily have vascular dementia. Secondly and inversely, dementia could be missed in a patient with a physical handicap whose defective mental functions go unnoticed both by his family and physician. Unlike Alzheimer's disease where neuropsychological problems predominate because these patients retain good physical autonomy for a long time, patients with vascular dementia are not explored routinely for neuropsychological disorders which may be hidden by more obvious neurological symptoms. Such disorders, especially gait disorders, are however the key to diagnosis. Mixed dementia is a third pitfall. This concept is based on histological findings and should not be used as a "catch-all" category. During the patient's lifetime diagnosis is probably impossible; current clinical scales do not take it into consideration.