Dementia is one of the most frequent and disabling health problems of our times. During the past twenty years, we have witnessed growing public and professional interest in dementia, its diagnosis and causes. This has led to the introduction of better methods of detection of cognitive impairment, coupled with early diagnosis of Alzheimer's disease and, to a lesser degree, of other forms of dementia. However, if the clinical presentation of patients does not follow the typical pattern of progressive memory loss starting in later life, then currently available diagnostic methods are less likely to be useful and patients with dementia may go unidentified for prolonged periods of time. Some of the less frequent causes of dementia may initially present with psychological or behavioral disturbances, others are associated with prominent neurological signs and symptoms. Patients may also present with marked deficits in cognitive domains other than memory, such as impaired language, which makes the diagnostic workup more difficult and onerous.