The clinical diagnosis of dementia includes medical history, neurological examination, psychiatric interview and dementia scale. The identification of conditions producing dementia can only be achieved by adding to the clinical information the data gathered from ancillary investigations. The usual ancillary diagnostic investigations (biochemical tests, cerebrospinal fluid (CSF), EEG, CT, MRI, angiography) can rather easily identify brain disorders due to tumors, vascular malformations, hematomas, infections, toxins and drugs, deficiency diseases, normal-pressure hydrocephalus, metabolic and endocrine derangements. The differential diagnosis between degenerative and vascular dementia needs laboratory tests such as CSF, EEG, Somatosensory Evoked Potentials, CT (which constitutes a major role in a modified ischemic score) and MRI. The three final diagnostic labels are possible, probable and definite vascular dementia, which include clinical features and laboratory investigations concurrently confirming the diagnosis. If ancillary investigations fail to show multiple infarct lesions or if mixed forms are suspected an unequivocal diagnosis can be made only on histopathological evidence.