Generalized anxiety disorder (GAD) is a prevalent and disabling disorder characterized by persistent worrying, anxiety symptoms, and tension. It is the most frequent anxiety disorder in primary care, being present in 22% of primary care patients who complain of anxiety problems. The high prevalence rate of GAD in primary care (8%) compared to that reported in the general population (12-month prevalence 1.9–5.1%) suggests that GAD patients are high users of primary care resources. GAD affects women more frequently than men and prevalence rates are high in midlife (prevalence in females over age 35: 10%) and older subjects but relatively low in adolescents. The natural course of GAD can be characterized as chronic with few complete remissions, a waxing and waning course of GAD symptoms, and the occurrence of substantial comorbidity particularly with depression. Patients with GAD demonstrate a considerable degree of impairment and disability, even in its pure form, uncomplicated by depression or other mental disorders. The degree of impairment is similar to that of cases with major depression. GAD comorbid with depression usually reveals considerably higher numbers of disability days in the past month than either condition in its pure form. As a result, GAD is associated with a significant economic burden owing to decreased work productivity and increased use of health care services, particularly primary health care. The appropriate use of psychological treatments and antidepressants may improve both anxiety and depression symptoms and may also play a role in preventing comorbid major depression in GAD thus reducing the burden on both the individual and society. Depression and Anxiety 16:162–171, 2002. © 2002 Wiley-Liss, Inc.