Positron emission tomography (PET) measurements of cerebral glucose use were made in 18 patients with generalized anxiety disorder (GAD) during a passive viewing task off medication, and an active vigilance viewing task before and after medication or placebo treatment. In the passive viewing task, patients with GAD were compared with 15 normal controls. A significant difference in pattern of absolute brain metabolism was found. Patients showed lower absolute metabolic rates in basal ganglia and white matter. Relative metabolism was increased in the left inferior area 17 in the occipital lobe, right posterior temporal lobe, and the right precentral frontal gyrus. Significant left-right asymmetry of the parahippocampal gyri was not found in patients with GAD. An active vigilance task resulted in activation of relative basal ganglia metabolism in patients. Benzodiazepine therapy resulted in decreases in absolute metabolic rates for cortical surface, limbic system, and basal ganglia and was not associated with normalization of patterns of glucose metabolism. Change in anxiety scores was significantly correlated with change in limbic system and basal ganglia for the placebo group. The normal-anxious difference in the basal ganglia and the change seen in this region after benzodiazepine treatment are suggestive of a role in anxiety for this structure.