Ten patients are described exemplifying a syndrome characterized by intermittent oscillations of the eyes, severe body tremulousness, and evidence of a benign encephalitis. The ocular movements accord with the definition of opsoclonus. The body tremulousness is related to posture but without other cerebellar signs. The encephalitis is mild and manifest chiefly by pleocytosis in the cerebrospinal fluid. The disease usually follows in the wake of an upper respiratory infection and resolves characteristically without sequela within a few weeks' time. Attempts to recover a virus have been uniformly unsuccessful.