Alzheimer's disease (AD) poses a major clinical challenge because of its high prevalence in the aging population, its prolonged course, and the absence of curative treatment. Important advances have recently been made, however, in the diagnosis of the disease and the elucidation of its neuroscientific basis. Genetic research has identified an allele of apolipoprotein E that may confer a higher risk of developing AD. In addition, new possibilities for treatment are being investigated. One drug therapy--tacrine--has been approved, although uncertainty lingers about its efficacy and safety. In the absence of effective medical treatment, AD is a difficult problem for patients and their families. However, the physician can help by providing emotional support, symptom management, and informed counseling.