Myoclonus is a very rapid, jerking, hyperkinetic movement disorder of the limbs, which is often bilateral. Myoclonus is stereotyped, repetitive, and unsuppressible. Myoclonus may originate from the cerebral cortex, brainstem, or spinal cord, and its differential diagnosis is extensive.55 Myoclonus in isolation in a child is not necessarily an ominous sign. The occurrence of myoclonus immediately after birth or in the neonate is benign and almost always resolves spontaneously.56,57 Nocturnal myoclonus is a normal variant that is very common in the general population. Additionally, myoclonus may be noted with metabolic derangements or in association with medications. Opsoclonus-myoclonus syndrome is characterized by rapid, involuntary, chaotic conjugate movements of the eyes, accompanied by myoclonus. The eye movements can be horizontal, vertical, or rotatory, and they are often accompanied by oscillopsia, or the sensation the world is moving. Like Sydenham chorea, opsoclonus-myoclonus is thought to be autoimmune in origin, and more than half of the pediatric patients with opsoclonus-myoclonus syndrome have underlying neuro-blastoma.58 Other potential associations with opsoclonus may include parainfectious encephalitis, systemic diseases such as celiac disease or AIDS, side effects of medications, or toxins. Myoclonus can also be an associated finding in a variety of neurological syndromes including myoclonus dystonia (DYT-11) and certain forms of epilepsy (juvenile myoclonic epilepsy, Lennox-Gastaut syndrome); therefore, the occurrence of other neurological abnormalities in addition to myoclonus should prompt consideration of such an underlying diagnosis.