Benign myoclonus of early infancy, first described by Fejerman and Lombroso, is a paroxysmal phenomenon of the first 2 years of life which occurs in neurologically healthy infants during wakefulness, and is usually triggered by excitement or frustration. We studied the neurophysiological features of the phenomenon in five children, aged 7 to 11 months, who were monitored by video-EEG recording, and by polygraphic recording in 3 of the 5 cases. The phenomenon is characterized by a shudder-type, paroxysmal motor manifestation involving mainly the trunk and sometimes the head, associated with tonic limb contractions of variable intensity, from hardly noticeable to more sustained. The EEG counterpart never showed modifications, the polygraphic study demonstrated a brief tonic limb contraction. The clinical manifestation should not be confused with the spasms of epileptic infantile spasms syndrome, or with tonic reflex seizures of early infancy. Although the phenomenon is already widely known, its polygraphic recording is rarely reported in literature. The polygraphic data of our patients contributes to the diagnosis and understanding of the pathophysiology of this paroxysmal manifestation.