To a certain extent the dementias have been forgotten diseases until just recen tly when they were brought to the attention of the general public and health authorities as a result of the increasing number of cases in the aging popula tion, especially among famous people, and because of the efforts of private foundations. The goals of the present volume are to present the dementias to health prac titioners, to provide some basic information on their epidemiology and biolo gical basis and to discuss the diagnostic and clinical problems that physicians and institutions face when caring for demented patients. This book explores the various types of dementias and is not limited to Alzheimer's disease although, as expected, more information is available and presented on this pathology. On the other hand, a few fundamental questions on dementia can only be answe red through a comparison of the various forms. Examples of such questions are the following: Is the loss of cerebral tissue sufficient to cause dementia? Are there thresholds or is there a continuous progression toward the irreversible development of dementia? Are there common pathways in the dementing pro cess? Are there common risk factors? Comparative analysis allows the common and distinctive patterns of the various dementias to be defined, ultimately lea ding to more focused therapeutic interventions.