Delirium is highly prevalent in cancer patients with advanced disease.Frequently a preterminal event, the condition is a sign of significantphysiologic disturbance, typically involving multiple medical etiologiesincluding infection, organ failure, adverse medication effects,and in rare situations, paraneoplastic syndromes. Unfortunately, deliriumis frequently underrecognized or misdiagnosed and, therefore,inappropriately treated or untreated in terminally ill patients. The clinicalfeatures of delirium are numerous and encompass a variety of neuropsychiatricsymptoms common to other psychiatric disorders. Threeclinical subtypes of delirium, based on arousal disturbance and psychomotorbehavior, have been described: hyperactive, hypoactive, andmixed. The differential diagnosis for delirium includes depression,mania, psychosis, and dementia. Numerous instruments have been developedto aid the clinician in rapidly screening for the disorder. Standardmanagement requires an investigation of the etiologies, correctionof the contributing factors, and management of symptoms. Symptomaticand supportive therapies, including numerous pharmacologicapproaches, are important, but several aspects of the use of neurolepticsand other agents in the management of delirium in the dying patientremain controversial.