Anxiety disorders are chronic illnesses that occur more often in women than men. Previously, we found a significant sex difference in the 5-year clinical course of uncomplicated panic disorder that was attributable to a doubling of the illness relapse rate in women compared to men. However, we have not detected a sex difference in the clinical course of panic with agoraphobia, generalized anxiety disorder (GAD), or social phobia (SP), which are conditions generally thought to be more chronic than uncomplicated panic disorder. Given that a longer follow-up period may be required to detect differences in clinical course for more enduring illnesses, we conducted further analyses on this same cohort after a more protracted interval of observation to determine whether sex differences would emerge or be sustained. Data were analyzed from the Harvard/Brown Anxiety Research Program (HARP), a naturalistic, longitudinal study that repeatedly assessed patients at 6 to 12 month intervals over the course of 8 years. Data regarding remission and relapse status were collected from 558 patients and treatment was observed but not prescribed. Cumulative remission rates were equivalent among men and women with all diagnoses. Patients who experienced remission were more likely to improve during the first 2 years of study. Women with GAD continued remitting late into the observation period and experienced fewer overall remission events by 8 years. However, the difference in course failed to reach statistical significance. Relapse rates for women were comparable to those for men who suffered from panic disorder with agoraphobia, GAD, and SP. Again, initial relapse events were more likely to occur within the first 2 years of observation. However, relapse events for uncomplicated panic in women were less restricted to the first 2 years of observation and by 8 years, the relapse rates for uncomplicated panic was 3-fold higher in women compared with men. Anxiety disorders are chronic in the majority of men and women, although uncomplicated panic is characterized by frequent remission and relapse events. Short interval follow-up shows sex differences in the remission and relapse rates for some but not all anxiety disorders. These findings suggest important differences in the clinical course among the various anxiety disorders and support nosological distinctions among the various types of anxiety. It may be that sex differences in the clinical course of anxiety disorders hold prognostic implications for patients with these illnesses. Depression and Anxiety 17: 173–179, 2003. © 2003 Wiley-Liss, Inc.