Delirium has been found to occur in 25% to 40% of patients with cancer at some time during their illness and has been reported to be as high as 85% in patients with advanced disease. The cognitive and behavioral changes associated with delirium cause emotional distress to the patient and family. More seriously, delirium can lead to dementia or death if untreated. The initial stages of delirium are frequently confused with anxiety. The nurse plays a crucial role in the identification of delirium. Effective intervention requires early assessment of the etiology of delirium and its associated cognitive impairments. Some of the physiological sources are: vascular, metabolic, infectious, respiratory, and cerebral disorders. Analgesics, chemotherapeutic agents, and other medications can also cause delirium. Additionally, recent clinical reports identify monoclonal antibodies, interleukin 2, and ifosfamide as contributing to delirium. In order to adequately differentiate anxiety from delirium, the nurse assesses cognitive functioning which includes attention-concentration, recent memory, orientation to immediate environment, and sensory-perceptual functions. Nursing interventions are directed toward organizing the patient's environment and providing reassurance to the patient and family. Collaboration with the medical team is essential in treatment of the underlying organic causes. Patient outcomes serve as the evaluation criteria for the effectiveness of nursing interventions. This presentation offers a standard of care which describes the nursing diagnoses associated with delirium, specific assessment criteria, interventions, and expected patient outcomes. Delirium represents a quality of life issue. This standard of practice provides the means for the nurse to have an impact on the patient's and family's quality of life.