1. Panic disorder (PD) is an illness that can be acute or chronic and is often complicated by depression, phobias and obsessions. This illness affects at least 10% of the population. 2. Panic disorder has been recognized as a psychopathologic condition for at least 100 years. Over the last several decades, health professionals have changed their view of PD and in 1987 the DSM-III included PD as a distinctive syndrome. 3. Several studies have shown PD to be a chronic illness with only little to no improvement in 36 – 40% of the subjects after 1 to 20 years of treatment. Studies also suggest that duration of illness affects the degree of impairment: subjects who had PD for more than 6 months showed more impairment that subjects who had PD for less than 6 months. 4. Several studies show that 50–75% of patients with PD have had at least one episode of major depression. Findings also indicate that subjects with both PD and secondary depression are a more severely ill group. 5. The HARP study is an ongoing 12-site naturalistic, longitudinal examination of patients with current or past PD. One of the major goals of this study is to describe the patterns of the clinical course of PD related disorders. 6. Clinical experience indicates that an estimated 40% of PD patients may need treatment for one year and between 20–40% will require continued maintenance treatment. Long-term treatment may include behavioral therapy and/or medication. 7. Anxiety disorders are common and familial and are consistently higher among women. Panic Disorder is a chronic condition frequently complicated by Axis I and II disorders. Continued long-term maintenance studies of medications and psychotherapy for anxiety disorders is critical in the treatment of this chronic illness.