Alternating hemiplegia of childhood is a rare syndrome characterized by onset before 18 months of age of frequent attacks of alternating paralysis, transient ocular palsies, nystagmus, choreoathetosis, and autonomic dysfunction. We describe features of 10 patients followed for up to 27 years. The mechanism of alternating hemiplegia remains unknown but an association to migraine is suspected because of the strong family history of migraine and aura symptoms in some patients. We treated nine patients with flunarizine, a calcium channel blocker, for up to 5 years; they showed a reduction in duration of the hemiplegic attacks, but the episodes ceased completely in only one patient. With long-term follow-up, the persistent motor, movement, and cognitive deficits are more apparent. It is not certain if the flunarizine alters this course.