In infants with benign neonatal sleep myoclonus, myoclonus was bilateral, synchronous and repetitive, located primarily in the distal parts of the upper extremities and directed toward flexion of fingers, wrist, and elbow. Ankle dorsiflexion myoclonus was also present in two infants. In infants with myoclonic jerks can be repeated for a prolonged period and have been noted to occur for up to 30 minutes continuously in some patients. Infant myoclonus has also occurred synchronously with repetitive sound stimulus.