Alternating skew on lateral gaze (bilateral abducting hypertropia).

We report thirty-three patients with alternating skew deviation on lateral gaze. The right eye was hypertropic in right gaze, and the left eye was hypertropic in left gaze. Most patients had associated downbeat nystagmus and ataxia and were diagnosed as having lesions of the cerebellar pathways or the cervicomedullary junction. This contrasts with a previous report in which alternating skew was seen mainly in lesions of the midbrain pretectum.