It is important to classify myoclonus into cortical, subcortical and spinal myoclonus especially from the view point of treatment, because cortical myoclonus is usually more severe than myoclonus of other categories. And patients with cortical myoclonus often develop generalized convulsion seizures. Since most myoclonus depending on enhancement of neuronal activities which are inherently present in normal subjects, electrophysiological studies are useful for elucidating the underlying pathophysiological mechanisms and correct diagnosis. The main neurophysiological tests that could detect origin of myoclonus are Video-EEG monitoring and somatosensory evoked potential which is a confirmatory test for cortical myoclonus. The aim of this study is to detect reliability of video-EEG in detecting the origin of myoclonus for proper diagnosis and prognosis. The subjects included were: Forty seven patients (21 males and 26 females) selected from the Neurology outpatient clinic Kasr Al-Eini Hospital presented clinically by idiopathic myoclonus. Their age ranging from 11 to 51 years. Conclusion: To determine the generator of myoclonus, clinical as well as neurophysiological features have to be taken into account. Once spinal or cortical origin has been excluded, myoclonus may be subcortical in which no positive arguments for its topography. Extensive neurophysiologic studies in each myoclonic patient appear to be a hard & time consuming work, however the net results of these studies deserved to be hardly studied to reach proper diagnosis for reaching right way in treatment. Video EEG (and JLBA) are more sensitive tool for diagnosing physiological type of myoclonus, accordingly giving correct treatment. Routine conventional EEG may be of value in general diagnosis of myoclonus, but has no the same role as Video EEG & in the diagnosis of type of myoclonus. However conventional EEG is of value in the diagnosis and follow-up of patients with metabolic, degenerative or epileptic forms of myoclomc disorders. Demonstration of EEG SSW or PSSW in association with myoclonus usually suggests its cortical origin, but absence of them in association with myoclonus does not entirely exclude the possibility of cortical origin. On the other hand, myoclonus of subcortical or spinal cord origin is not associated with any special EEG phenomena. Demonstration of giant SSEP is of significant value for supporting the clinical diagnosis of cortical myoclonus. However absent giant reflex no exclude cortical myoclonus, so investigator should proceed to SSEP recovery cycle & C- reflex studies.