Perfusion- and diffusion-weighted magnetic resonance imaging was performed during spontaneous visual auras in four migraineurs. Alterations in relative cerebral blood flow (16-53% decrease), cerebral blood volume (6-33% decrease), and tissue mean transit time (10-54% increase) were observed in the gray matter of occipital cortex contralateral to the affected visual hemifield. No changes in the apparent diffusion coefficient were observed either while the patients were symptomatic or after resolution of the visual symptoms but before the onset of headache. Functional magnetic resonance imaging can be a useful noninvasive tool to study hemodynamic changes during spontaneous attacks of migraine with aura.