The anatomical localisation of the abnormality underlying opsoclonus-polymyoclonus-the "Dancing Eye Syndrome"-is uncertain and both the brainstem and cerebellum have been implicated. We used electrooculographic recordings to assess the eye movements in five children with this syndrome. Overshoot dysmetria was the consistent feature for the saccades of all five cases. One patient was also assessed after the main symptoms of ataxia and opsoclonus (saccadic oscillations, without an intersaccadic interval) had resolved and the saccades were found to remain hypermetric. Smooth pursuit and optokinetic nystagmus were normal, although the opsoclonus occurred throughout the recording session and were superimposed upon the normal eye movement waveforms. The vestibulo-ocular reflex was normal in four patients, but in one case, the time-constant was significantly prolonged: this has only been reported in experimental lesions of the nodulus in monkeys. The presence of saccadic overshoot dysmetria is highly suggestive of a cerebellar origin for the abnormal eye movements in these children. However, the preservation of normal smooth pursuit and the absence of gaze-paretic, rebound and downbeat nystagmus, implies the sparing of the flocculus and paraflocculus. We propose that the origin of these oculomotor deficits could be the cerebellar fastigial nuclei.