Delirium, an acute decline in attention and cognition, is a common and potentially life-threatening condition among older adults (65 years and older). It often leads to a cascade of events, including loss of independence, increased morbidity and mortality, and higher healthcare costs. Delirium is particularly prevalent in hospitalized older patients, affecting 14-24% at admission and 6-56% during hospitalization. It complicates hospital stays for 20-50% of older hospitalized patients, increasing costs by $2,500 per patient and contributing to about $6.9 billion in Medicare hospital expenditures in 2004. Delirium also has a significant impact on post-discharge care, leading to institutionalization, rehabilitation, and informal caregiving. The diagnosis of delirium is primarily clinical, based on careful bedside observation. Delirium can be hypoactive or hyperactive, with the hypoactive form being more common and often underrecognized. The etiology of delirium is multifactorial, involving a vulnerable patient (with predisposing factors) and precipitating factors or noxious insults. Pathophysiology includes cholinergic deficiency, dopaminergic excess, and inflammation. Preventive strategies include multicomponent approaches to reduce risk factors, such as cognitive impairment management, early mobilization, and nonpharmacologic interventions. Management of delirium involves addressing all evident causes, providing supportive care, and treating behavioral symptoms. Pharmacologic management is reserved for cases where symptoms threaten safety or essential therapy. Delirium and dementia are highly interrelated, with dementia being the leading risk factor for delirium. Delirium can worsen functional status and outcomes in patients with dementia, and it may serve as an early indicator of cognitive decline. Delirium is also an indicator of the quality of healthcare, with many cases being preventable through improved care processes.Delirium, an acute decline in attention and cognition, is a common and potentially life-threatening condition among older adults (65 years and older). It often leads to a cascade of events, including loss of independence, increased morbidity and mortality, and higher healthcare costs. Delirium is particularly prevalent in hospitalized older patients, affecting 14-24% at admission and 6-56% during hospitalization. It complicates hospital stays for 20-50% of older hospitalized patients, increasing costs by $2,500 per patient and contributing to about $6.9 billion in Medicare hospital expenditures in 2004. Delirium also has a significant impact on post-discharge care, leading to institutionalization, rehabilitation, and informal caregiving. The diagnosis of delirium is primarily clinical, based on careful bedside observation. Delirium can be hypoactive or hyperactive, with the hypoactive form being more common and often underrecognized. The etiology of delirium is multifactorial, involving a vulnerable patient (with predisposing factors) and precipitating factors or noxious insults. Pathophysiology includes cholinergic deficiency, dopaminergic excess, and inflammation. Preventive strategies include multicomponent approaches to reduce risk factors, such as cognitive impairment management, early mobilization, and nonpharmacologic interventions. Management of delirium involves addressing all evident causes, providing supportive care, and treating behavioral symptoms. Pharmacologic management is reserved for cases where symptoms threaten safety or essential therapy. Delirium and dementia are highly interrelated, with dementia being the leading risk factor for delirium. Delirium can worsen functional status and outcomes in patients with dementia, and it may serve as an early indicator of cognitive decline. Delirium is also an indicator of the quality of healthcare, with many cases being preventable through improved care processes.