This chapter concerns palatal myoclonus. Indeed Spencer's vivid nystagmus is now abandoned in favor of the less ambiguous myoclonus. The clinical data are reviewed: its appearance, rhythmic frequency, delay with respect to the causal lesion, resistance to most external influences, and possible associations. The most frequent lesion associated with this clinical phenomenon is a special type of degeneration with hypertrophy of the olivary nucleus of the medulla oblongata, on the side opposite the myoclonus when it is unilateral. This degeneration is usually secondary to a primary lesion, located either in the ipsilateral (to the hypertrophied olive) central tegmentum tract or in the contralateral dentate nucleus, through a specific dentatoolivary pathway. The probable existence of this pathway is confirmed by the demonstration of a topographic relationship between dentate nucleus and contralateral inferior olive and by its delineation in the vicinity of the red nucleus where the superior cerebellar peduncle crosses the central tegmental tract. The mechanisms of these lesions and their ensuing symptoms are discussed. It is suggested that there is a transsynaptic degeneration probably disclosing an archaic phenomenon. Few drugs influence this steady abnormal movement: 5-HTP and carbamazepine recently have been credited with some success.