Background: Several studies have shown that stellate ganglion block (SGB) is an effective treatment for certain cerebrovascular related diseases; however, the direct effect of SGB on the cerebral vasculature is still unknown. The present study investigated the effect of SGB on the cerebral vascular system using magnetic resonance angiography. Methods: Time-of-flight magnetic resonance angiography images of 19 healthy female volunteers (mean ages of 46.4± 8.9 yr) were obtained before and afterSGBwith 1.5-T magnetic resonance imaging. The authors determined successful interruption of sympathetic innervation to the head with the appearance of Horner syndrome and conjunctival injection. We measured changes in the average signal intensity and diameter of the major intracranial and extracranial arteries and their branches, which were presented with mean (±SE). Results: The signal intensity changes were observed mainly in the ipsilateral extracranial vessels; the external carotid artery (11.2%, P < 0.001) and its downstream branches, such as the occipital artery (9.5%, P < 0.001) and superficial temporal artery (14.1%, P < 0.001). In contrast, the intensities of the intracranial arteries did not change with the exception of the ipsilateral ophthalmic artery, which increased significantly (10.0%, P = 0.008). After SGB, only the diameter of the ipsilateral external carotid artery was significantly increased (26.5%, P < 0.001). Conclusions: We were able to observe significant changes in the extracranial vessels, whereas the intracranial vessels were relatively unaffected (except for the ophthalmic artery), demonstrating that both perivascular nerve control and sympathetic nerve control mechanisms may contribute to the control of intracranial and extracranial blood vessels, respectively, after SGB.