Transient cognitive disorders (delirium and pseudodelirium) are highly prevalent among the elderly, especially those with brain damage. Delirium is a common feature of physical illness or drug intoxication in elderly patients and requires prompt medical attention. While potentially reversible, delirium may herald death. Pseudodelirium may be induced by psychosocial stress or accompany a functional mental disorder. Transient cognitive disorders must not be confused with dementia, a chronic syndrome. The author discusses clinical features, etiology, pathogenesis, diagnosis, and treatment of delirium and related transient disorders of cognition in the elderly.