The early diagnosis of vertebrobasilar insufficiency in patients with vertigo as their only symptom was attempted using a battery of vestibulo-oculomotor tests. With this testing procedure, we were able to find abnormal vestibulo-oculomotor mechanisms that could account for the vertigo in 41 of 42 patients. These abnormalities, however, did not fall into an easily recognizable pattern that could be considered characteristic of vertebrobasilar insufficiency. The large intersubject variability probably arises from the very different and widespread lesions that occur at the vestibular and neurological levels as a consequence of vertebrobasilar insufficiency.