A rare form of secondary parkinsonism has been recently described as 'hemiparkinsonism-hemiatrophy syndrome'. We report a case with such clinical features. A neurophysiological study of the evoked potentials, somatosensory and motor, has been conducted. We stress the neuroradiological findings at nuclear magnetic resonance, which documented the presence of an area of altered signal in the mesencephalon, between the cerebral pedunculus and the red nucleus on the right side. The etiopathogenetic considerations and diagnostic criteria are discussed. Moreover we evaluate the efficacy of levodopa therapy.