Dyspnea is a frequent and devastating symptom among advanced cancer patients and is often difficult to control. However, there has been considerably less emphasis in the literature on the appropriate characterization and management of this symptom than of other cancer-related symptoms. The purpose of this paper is to review issues relating to the prevalence, causes, prognosis and treatment of dyspnea in patients with advanced cancer. A Medline search of the literature published from 1966 to February 1999 was conducted. Dyspnea occurs in 21-78.6% of advanced cancer patients and is reported to be from moderate to severe in 10-63% of the patients. The frequency and severity of dyspnea increase with the progression of the disease and/ or when death is approaching. Lung cancer patients with dyspnea have shorter survival than patients with other types of cancer. Dyspnea can be a direct effect of the cancer, an effect of therapy or not related to the cancer or therapy. In addition to cancer, patients may suffer from chronic obstructive pulmonary disease, congestive heart failure, nonmalignant pleural effusion, pneumonitis, air flow obstruction, or bronchospasm associated with asthma. In the absence of lung or heart disease, dyspnea may be a clinical expression of the syndrome of overwhelming cachexia and asthenia or of severe asthenia. Many different causes may co-exist in a patient. Whenever possible, an attempt should be made to treat underlying cancer. Radiotherapy and chemotherapy may relieve dyspnea also in patients who fail to achieve a major objective response. Symptomatic measures in addition to specific treatments for the underlying cancer and/or other pulmonary and cardiovascular diseases are indicated. Oxygen therapy has proved effective in hypoxemic and nonhypoxemic patients. The role of transfusion therapy to relieve anemia-related dyspnea in advanced and terminal cancer patients is still controversial. Oral, subcutaneous and intravenous opioids are effective but underused in these patients, whereas currently available evidence does not support the clinical use of nebulized opioids. While benzodiazepines are frequently used in patients with dyspnea, these drugs were ineffective in four out of five randomized controlled trials. Other components of the symptom expression are better managed by supportive counseling, occupational therapy or physiotherapy. While the mechanism of breathing and the consequences of different pathologic conditions for both respiratory function and gas exchange are well known, the genesis and pathophysiology of dyspnea as a symptom are much less well understood. Palliative care assessment should be focused on dyspnea as a symptom rather than on the functional and gas exchange abnormalities. Increased research on the appropriate management of dyspnea is needed.