Background <p>The geometric characteristics of the vertebrobasilar artery (VBA) have been suggested to be associated with posterior circulation hemodynamics and vascular morphology. Therefore, this prospective study aimed to explore the influence of geometric parameters of VBA on vertebrobasilar system (VBS) geometries and basilar artery (BA) curvature in normal adults.</p> Methods <p>Four hundred healthy volunteers (≥ 18 years) underwent routine MRI sequences (plain scan, DWI, 3D-TOF-MRA); 239 with no abnormal signals were included. We measured vertebral artery (VA) diameters, VA angles, mid-basilar artery (BA) angle, BA curvature direction/degree, and the angle between VAs (VV angle) on 3D-TOF-MRA. The VA angle most associated with BA curvature was defined as the dominant VA angle. Vertebrobasilar system (VBS) geometries were classified into four configurations: Tuning Fork, Walking, Dominant-λ, and Hypoplasia-λ. Correlations between VBA geometry parameters, VBS configurations, and BA curvature were analyzed.</p> Results <p>(1) Cohort: 239 volunteers (mean age 26 [23–36] years; 89 males); (2) Configuration differences: Walking vs. Tuning Fork showed significant differences in absolute VA angle difference, mid-BA angle, dominant VA angle, and VV angle (<i>P</i> &lt; 0.05); (3) BA curvature direction: Significantly associated with the dominant VA angle side in Walking and Tuning Fork (<i>P</i> &lt; 0.001), and with the larger VA diameter side in Dominant-λ and Hypoplasia-λ (combined with VA course direction, <i>P</i> &lt; 0.001); (4) BA curvature degree: Positively correlated with mid-BA angle, and VV angle (<i>P</i> &lt; 0.05), age showed an association with BA curvature degree in unadjusted analysis, but did not remain significant after FDR correction; mid-BA angle showed the strongest association with curvature magnitude (β = 0.976, <i>P</i> &lt; 0.001).</p> Conclusion <p>Geometric parameters of the VBA were associated with variations in VBS geometries and BA curvature.</p>