Anxiety sensitivity refers to fears of anxiety-related sensations. Most often measured by the Anxiety Sensitivity Index (ASI), anxiety sensitivity is a dispositional variable especially elevated in people with panic disorder. Regardless of diagnosis, ASI scores often predict panic symptoms in response to biological challenges (e.g., carbon dioxide inhalation) that provoke feared bodily sensations. Prospective longitudinal studies indicate that scores on the ASI predict subsequent spontaneous attacks, indicating that elevated anxiety sensitivity is a risk factor for panic and perhaps panic disorder. Cognitive behavioral treatment reduces anxiety sensitivity in panic patients, perhaps protecting against relapse. Imipramine likewise decreases anxiety sensitivity.