Generalized anxiety disorder (GAD) is a common and serious disorder. Despite this fact, there is no clear understanding of the exact neurobiological changes underlying the condition. To date, there are few studies of neurobiological function in patients with GAD, and only limited comparative data with depression are available. Advances in neuroanatomical imaging techniques are beginning to allow detailed study of regional blood flow and metabolism and may offer insights into the specific regions of the brain involved in GAD. Investigations into neurotransmitter dysfunction have implicated the gamma-aminobutyric acid/benzodiazepine, serotonergic, and noradrenergic systems in this disorder. Variations in sleep patterns have also been assessed and indicate a biological separation from depression.