We studied clinically and electrophysiologically 8 patients affected by orthostatic tremor (OT), which is an unusual movement disorder consisting of shaking movements of the legs and trunk in the standing position. We failed to find any cause in 6 of the 8 cases. In 2 patients OT was clearly secondary to neurologic disease: hydrocephalus due to non-tumoral aqueduct stenosis and chronic relapsing polyradiculoneuropathy. The findings obtained suggest a relationship between OT and essential tremor (ET).