Alternating hemiplegia is a rare neurological disorder that develops in childhood, usually before the first 4 years. The disorder is characterized by recurrent but temporary episodes of paralysis on one side of the body. The paralysis can affect eye movements, limbs, or facial muscles. One form of the disorder, identified very recently, has a favorable outlook. It occurs primarily at night, when a child awakens, and is apparently related to migraine. These children have no other mental or neurological impairments. In more serious cases symptoms may include mental impairment, balance and gait difficulties, excessive sweating, and changes in body temperature. Seizures can occur. Sleep helps in the recovery from the periods of paralysis but the paralysis can recur upon waking. The cause of the disorder is unknown.