OBJECTIVE Our aim in this study was to compare headache-free and spontaneous migraine measurements of blood flow velocity and the pulsatility index in the anterior cerebral artery, middle cerebral artery, and posterior cerebral artery. METHODS Thirty-one patients (nine having experienced migraine with aura and 22 migraine without aura) were studied in headache-free periods and during spontaneous migraine attacks with transcranial Doppler ultrasonography. RESULTS During attacks of migraine with aura, blood flow velocities (particularly the diastolic velocity [p = 0.05]) were reduced while the pulsatility index increased (p = 0.05), whereas a generalized increase in diastolic velocity (p less than 0.02) and a decrease in the pulsatility index (p = 0.05) were observed during attacks of migraine without aura. Significant variations of blood pressure and heart rate were never found. CONCLUSIONS These findings are consistent with constriction of resistance vessels in migraine with aura and dilatation of the vessels in migraine without aura. This disparity could be due to a difference between the two migraine types or could be related to the fact that in this study the time interval between headache onset and transcranial Doppler was shorter in the migraine-with-aura group. The latter explanation would apply if, in fact, both types of migraine evolve from hypoperfusion to hyperperfusion during their time course, although perhaps with a difference in intensity.