We reviewed the clinical histories, examinations and results of quantitative vestibular testing in 91 patients with migraine-associated dizziness. Nausea and vomiting, hypersensitivity to motion and postural Instability accompanied the dizziness. In the majority of patients, the temporal profile of the dizziness was more typical of the headache phase of migraine than of the aura phase. Nineteen patients (20.9%) had unilateral hypoexcitability to caloric stimulation, which represents a modestly increased risk of damage to the peripheral vestibular apparatus. We propose two separate pathophysiologic mechanisms for the production of dizziness with migraine: Short-duration vertiginous attacks lasting minutes to 2 hours and temporally associated with headache are due to the same mechanism as other aura phenomena (spreading wave of depression and/or transient vasospasm). Longer-duration attacks of vertigo and motion sickness lasting days, with or without headache, result from the release of neuroactive peptides into peripheral and central vestibular tructures, causing an increased baseline firing of primary afferent neurons and increased sensitivity to motion.