Negative myoclonus (NM) is a motor phenomenon characterized by involuntary jerky movements due to a brief, sudden interruption of muscular activity. This motor disturbance can be observed in a variety of clinical conditions, that can range from physiological NM, occurring when falling asleep or after prolonged exercise, to asterixis, a form of NM observed in patients with toxic-metabolic encephalopathies or with focal brain lesions, or, as a paroxysmal phenomenon, labelled as epileptic negative myoclonus, in epileptic patients. Neurophysiological investigations are essential to diagnose NM and to distinguish it from other motor disorders, such as tremor or positive myoclonus. Furthermore, neurophysiological findings can provide useful information supporting a subcortical or cortical origin of NM. In cortical NM, recent data suggest a role of cortical active inhibitory areas in the generation of this motor phenomenon.