Using positron emission tomography with [18F]fluoro-2-deoxyglucose, we determined the regional cerebral metabolic rate of glucose utilization at rest in 8 medication-free patients with essential tremor and in 10 normal subjects. Taking the metabolic values of regions of interest as ratios to the mean hemispheric metabolism, the patients showed significant glucose hypermetabolism of the medulla and thalami, but not of the cerebellar cortex. This study lends support to earlier suggestions that circuits involving the inferior olivary nuclei in the medulla and the thalmus are involved in the generation of essential tremor.