As the population ages, increasing numbers of patients will present with dementia. Diagnosis may be very straightforward, as in an individual with dementia secondary to an obvious medical illness. However, the differential diagnosis of dementia may be less clear. Diagnostically challenging cases tend to appear in the setting of dementias that present without distinctive neurologic signs or evidence of medical or neurologic disease, such as Alzheimer's disease or the frontotemporal dementias. A similar diagnostic challenge is seen in dementias that present with neurologic signs but without obvious significant medical disorders, such as the parkinsonian dementias or the vascular dementias. In recent years, the presentations of these dementias have become more sharply drawn on the basis of consensus reviews of clinicopathologic correlations. Because each of these disorders has unique treatment and management strategies, the ability of clinicians to differentiate among these syndromes has become critically important.