Dyspnea frequently accompanies a variety of cardiopulmonary abnormalities. Although dyspnea is often considered a single sensation, alternatively it may encompass multiple sensations that are not well explained by a single physiologic mechanism. To investigate whether breathlessness experienced by patients represents more than one sensation, we studied 53 patients with one of the following seven conditions: pulmonary vascular disease, neuromuscular and chest wall disease, congestive heart failure, pregnancy, interstitial lung disease, asthma, and chronic obstructive pulmonary disease. Patients were asked to choose descriptions of their sensation(s) of breathlessness from a dyspnea questionnaire listing 19 descriptors. Cluster analysis was used to identify natural groupings among the chosen descriptors. We found that patients could distinguish different sensations of breathlessness. In addition, we found an association between certain groups of descriptors and specific conditions producing dyspnea. These findings concur with those in an earlier study in normal volunteers in whom dyspnea was induced by various stimuli. We conclude that different types of dyspnea exist in patients with a variety of cardiopulmonary abnormalities. Furthermore, different mechanisms may mediate these various sensations.