Background: Bilateral high-grade internal carotid artery (ICA) stenosis is critical for brain perfusion, and mechanisms of cerebral infarct induced by bilateral high-grade ICA stenosis can be investigated by the infarct patterns on diffusion-weighted imaging (DWI). Methods: From January 2006 to October 2010, we retrospectively enrolled 21 acute infarct patients with bilateral high-grade ICA stenosis. The infarct patterns were divided into territory, cortical border-zone and internal border-zone by DWI. Results: The milder ICA stenosis side had a lower risk of ischemic stroke (4 of 20). None of the 8 patients with bilateral severe ICA stenosis (70–99%) suffered ischemic stroke ipsilateral to the milder ICA stenosis side. No single infarct mechanism was prominent: 10 of 21 infarcts were cortical border-zone pattern, followed by internal border-zone (7 of 21) and territory. The difference in frequency of bilateral severe ICA stenosis between the three infarct mechanisms was not significant (p = 0.856). Conclusions: Cerebral infarcts occurred less frequently in the ipsilateral to milder ICA stenosis side, especially in bilateral severe ICA stenosis. The similar frequencies and hemodynamic status between the three infarct pattern groups indicated that both artery-to-artery emboli and being hemodynamically compromised contribute synergistically to bilateral ICA stenosis.