Periodic alternating nystagmus (PAN) is an ocular motor abnormality in which there is horizontal nystagmus that cyclically alternates direction, typically every few minutes. Most cases begin in adulthood, though occasionally, it begins in early childhood. Some cases of PAN appear to occur spontaneously (without any underlying cause), while other cases seem to be associated with specific diseases. Workup may include ocular motor studies (to document the eye movements) and brain MRI. There are no good treatments, though some patients benefit from baclofen.