OM is a rare condition with unilateral migrainous headache followed by ipsilateral ophthalmoplegia. Cranial nerves III, IV, or VI can be affected, but palsy of the oculomotor nerve (CNIII) is most frequent. Onset is typically in childhood. The headache may last for several days and ophthalmoplegia persists from several hours to weeks and months. Recovery can be incomplete, especially after repeated episodes. MRI typically reveals thickening and reversible contrast enhancement of the affected nerve when performed during acute ophthalmoplegia. Lesions in the cavernous sinus, the orbital fissure or the posterior fossa have to be ruled out. The pathogenesis of the disease is unclear but an inflammatory etiology has been suggested. The differenzial diagnosis includes neoplasm, trauma, aneurysm, and inflammatory processes such as Tolosa-Hunt syndrome or sarcoidosis.