Delirium, defined as an acute and sudden change in attention and overall cognitive function, is a substantial medical problem for older persons—and one that may be preventable. Patients ages 65 years and older account for almost half (49%) of all days of hospital care, and although delirium is the most frequent complication affecting this population, it often goes unrecognized. In fact, delirium affects over 2.5 million patients ages 65 and older during hospitalization annually (Inouye et al. 1999; U.S. Department of Health and Human Services 2004). Delirium is a costly condition, leading to increased costs per hospital stay of at least $2,500 per patient, which translates to $6.9 billion (values in U.S. dollars in 2004) of annual excess Medicare hospital expenditures directly related to delirium and its complications. Patients with delirium have a worse prognosis than patients without delirium and are at an increased risk of developing long-term cognitive and functional decline (Inouye 2006; Jackson et al. 2004), which in turn leads to additional posthospitalization treatment costs, such as for institutionalization, rehabilitation services, and home health care (Inouye 2006). Total health care costs related to delirium are estimated at $38 billion to $152 billion annually (Leslie et al. 2008).