Old age is a time of vulnerability to unintentional weight loss, a factor that is associated with increased morbidity and premature death. Many possible causes of weight loss in old age have been suggested. The so-called anorexia of aging may play a particular role, by either reducing food intake directly or reducing food intake in response to such adverse factors as age-associated reductions in taste and smell, poor dentition, use of multiple prescription medicines, and depression. Recent studies also raise the question of whether a reduction in dietary variety may be important. These findings emphasize the need for regular monitoring of body weight to detect unintentional weight loss in older individuals and suggest testable ways to minimize the impact of the anorexia of aging on body weight through improved dietary management.