Abstract: Objective To analyze the normal anatomical features of vertebrobasilar system (VBS), variation types and their relationship in the healthy subjects by 3.0T magnetic resonance angiography (MRA). 
Methods The original MRA images of 120 healthy volunteers were collected for maximum intensity projection (MIP) reconstruction, and normal anatomical features and variations of VBS were observed and recorded. The diameters of branches of VBS were measured and analyzed. 
Results Normal VBS accounted for 25% in healthy people. Types of variation included absence of the posterior inferior cerebellar artery (PICA), the anterior inferior cerebellar artery (AICA) and the posterior communicating artery (PCoA), repeated mutation of AICA and superior cerebellar artery (SCA), double origin of the posterior inferior cerebellar artery (DOPICA) on the right side, early bifurcation of SCA, anomalous origin of SCA,vertebral artery hypoplasia (VAH)，fetal posterior cerebral artery (fPCA) and basilar artery (BA) fenestration. The diameters of BA and right PCA of males were greater than those of females (P＜0.05), but there were no statistically significant difference in diameters of other blood vessels in different genders (P＞0.05). The most frequent variation was absence of the PICA, and absence of right PICA was more frequent than left PICA (P＜0.05). In cases with absence of PICA or AICA on one side, the proportion of well-developed or moderately-developed ipsilateral AICA or PICA was higher (P＜0.05). The VAH was more frequent on the right side (P＜0.05). The patency rate of bilateral PCoA in <45-year-old group were higher than ≥45-year-old group (P＜0.05). 
Conclusion The anatomical variation of the VBS is common and diverse, there is a compensatory relationship between several absent vessels, and the patency of PCoA is associated with age. These variations should warrant attention in the diagnosis and treatment of cerebrovascular diseases. 

Key words: basilar artery, magnetic resonance angiography, anatomy