Delirium is a frequent complication of cancer treatment and is associated with a high incidence of morbidity and mortality. This article summarizes recent literature on the epidemiology, mechanisms, and treatment of delirium in the patient with cancer. As data continue to emerge on risk factors and pathophysiological mechanisms, recognition of the distinctive features of delirium in specific cancer populations could contribute to a better understanding of consciousness, cognition, perception, and behavior during medical illness.