Patients with cancer frequently report dyspnea, the uncomfortable awareness of breathing. Lung involvement with cancer does not predict its occurrence. Patients describe it as one of the most frightening and distressing symptoms, and patient self-report is the only reliable measure. Measurements of respiratory rate, oxygen saturation, and arterial blood gases do not measure dyspnea. Opioids in modest doses have been demonstrated to give effective relief of dyspnea, whether or not identifiable reversible causes exist. Medical management of dyspnea can be directed at the underlying cause when the potential benefits outweigh the burdens of such treatment. In rare cases where symptomatic treatment is unable to control dyspnea to the patient's satisfaction, sedation is an effective, ethical option.