Although virtually all significant infections are discussed throughout this book, certain aspects of infectious diseases in older individuals need to be emphasized. This chapter stresses the unique aspects of infection in the elderly (defined here as older than 65 years of age). Infections that occur in long-term care institutions are briefly discussed. Infections in the aged are an important area of concern for medicine. The number of individuals who are older than 65 is increasing dramatically and is expected to double in the United States between 2010 and 2040. Although representing only 13% of the US population at present, the elderly consume 25% of all prescription medications and a similarly disproportionate amount of other healthcare services. With few exceptions (some viral infections and venereal diseases), most common infections occur more often in older individuals. Although mortality associated with many infections is increased in the elderly, age alone is now seen as a relatively unimportant risk factor for infection-related death or serious morbidity. Rather, it is the variety of comorbid conditions that are increasingly common with advancing age that appears to be closely associated with greater morbidity and mortality from infection. Since the early 1990s it has become clear that there is a general hyporesponsiveness of the immune system in elderly individuals. This is the most likely explanation for the muted symptoms and signs that are a common denominator of infections in the aged. In a number infectious illnesses maximum temperatures, white blood cell count elevations, and the overtness of clinical signs and symptoms are all less pronounced in older individuals. In clinical terms, this means that an elderly patient may have a serious bacteremic infection without chills, fever, or leukocytosis.