OBJECTIVES: The impact of artery geometry on intracranial atherosclerosis (ICAS) is unclear. To investigate the association between local artery geometry characteristics and middle cerebral atherosclerotic stenosis. METHODS: This was a case-control study. ICAS patients with more than 50% stenosis in one M1 pre-bifurcation segment but no significant stenosis on the other side were included. The stenosis degree, diameter, length, angle, and morphology (straight-shape, U-shape, and S-shape) of the M1 pre-bifurcation segments were measured by using digital subtraction angiography (DSA) combined with computed tomography angiography (CTA) and 3D reconstruction imaging. The geometry characteristics on both sides were compared. The conditional multivariate Logistics regression was used to investigate the association between stenotic sides and the geometry characteristics. RESULT: A total of 133 patients, 266 M1 pre-bifurcation segments, were included. Compared with non-stenotic sides, stenotic sides showed smaller diameters (2.873 ± 0.456 mm vs. 2.993 ± 0.360 mm, P = 0.002) and larger tortuosity index (7.61% vs. 6.45%, P = 0.048). The S-shape M1 pre-bifurcation segment was independently associated with the stenotic sides (OR = 3.509, 95% CI 1.176-10.468, P = 0.024). The stenotic side was worse fitted to Murray's law (mean square error 0.326 vs. 0.313). CONCLUSIONS: The morphology of the M1 pre-bifurcation segment was associated with middle cerebral atherosclerotic stenosis.