Reversible cerebral vasoconstriction syndrome (RCVS) is characterized by segmental vasoconstriction and dilatation of intracranial arteries, usually revealed by headaches, which spontaneously resolve in few weeks. We report a patient with RCVS, revealed by thunderclap headaches, involving both internal and external carotid artery (ECA). She received fluoxetin for depression and took a great amount of cannabis in the last months. While angio-MR, transcranial Doppler and CSF analysis were normal, cerebral angiography disclosed stenoses and dilatations of the middle cerebral artery. It also showed an involvement of maxillary arteries. Fluoxetin and cannabis were stopped. After few days, she had no more headaches. At 8th week, angiography was normalized confirming the RCVS. ECA angiogram may help reaching a diagnosis in patients with suspected RCVS when intracerebral abnormalities are minor or absent.