Anxiety disorders, the most common psychiatric conditions in the United States, have generated a great deal of research and scientific debate. Panic disorder, the best-studied anxiety disorder, is often believed to be either a biological disease or a psychological disease. The authors present a neuroanatomical model of panic disorder that attempts to reconcile these views. The model locates the three components of the disease--the acute panic attack, anticipatory anxiety, and phobic avoidance--in three specific sites of the CNS: the brainstem, limbic system, and prefrontal cortex, respectively. The authors suggest experiments to test their model.