Generalized anxiety disorder (GAD) is a chronic and highly prevalent disorder in the adult population, yet it remains a relatively poorly understood condition. Clinicians may be familiar with the symptoms of enduring excessive worrying, anxiety, and hypervigilance that are characteristic of GAD, but may not necessarily recognize that these are usually symptoms of a distinct psychiatric disorder. Despite changes in diagnostic criteria, estimates of prevalence for GAD are remarkably consistent across epidemiologic studies. Lifetime prevalence in the general population is estimated at 5% (DSM-III and/or DSM-III-R criteria), with rates as high as 10% among women aged 40 years and above, and cross-sectional rates among primary care attenders are about 8%, making GAD the most prevalent anxiety disorder in primary care. The age at onset of GAD differs from that of other anxiety disorders: prevalence rates are low in adolescents and young adults but increase substantially with age. Females are at greater risk than males, and the disorder is correlated with being unemployed or a housewife or having a chronic medical illness. GAD is frequently associated with comorbid depression and other anxiety and somatoform disorders. Significant GAD-specific disability occurs even when comorbidity is not present.