SYNOPSIS Potential availability of a reliable non‐invasive system for measuring regional cerebral blood flow (rCBF)prompted measurement of rCBF in patients with vascular headache in order to assess its diagnostic value. The rCBF in migraine varied with the clinical phase. During the prodrome phase the blood flow was reduced; whereas during the headache phase, a striking cortical hyperperfusion was noted. Patients who continued to have neurologic symptoms of the prodrome in the headache phase showed a mixed pattern of reduced and increased blood flow. The rCBF was found normal in the headache phase in patients with muscle contraction and psychogenic headache. In patients with headache as a prominent symptom of cerebrovascular insufficiency, rCBF was reduced but was not significantly different from rCBF in patients with cerebrovascular insufficiency without headache.