From a statistical analysis of a series of 214 cases of ruptured intracranial aneurysms, it was demonstrated that only four parameters among those collected on the admission day, are predictive of the final functional result: sex (p less than 0.001); age (p less than 0.02); clinical grade (p less than 0.001) and angiographic spasm (p less than 0.01). The surprisingly poor prognosis in women was explained by the higher frequency of spasm (p less than 0.005). Aneurysms in women predominated on the intracranial carotid artery (38%) and were frequently multiple (12%). A further angiographic study on 87 cases was then carried out including a systematic investigation of the cervical part of the vessels; it permitted one to identify angiographic features of fibromuscular dysplasia (FMD) on the cervical vessels in 20 cases. In those cases it was also observed that there was a marked female predominance (F/M = 5.6), a frequent localization on the internal carotid artery (50%), a high rate of multiple aneurysms (60%) and a poor prognosis related to spasm (50%). Therefore, intracranial aneurysms appear far more frequently than usually reported, to be related to FMD. The worse prognosis of ruptured intracranial aneurysms in females can be, at least partly explained by the association with FMD and the frequent occurrence of spasm. A careful investigation of patients exhibiting features of FMD in order to detect intracranial aneurysms before rupture, is suggested.