Background and Purpose- Endovascular treatment for acute intracranial atherosclerosis-related large vessel occlusion (ICAS [+]-LVO) is one of the challenging issues in modern mechanical thrombectomy era. We evaluated procedural and clinical outcomes of endovascular treatment for the ICAS (+)-LVO. We also compared their outcomes with those of large vessel occlusion not associated with intracranial atherosclerosis (ICAS [-]-LVO). Methods- We retrospectively reviewed consecutive patients with acute stroke who underwent endovascular treatment for LVO. Patients were assigned to the ICAS (+)-LVO group or the ICAS (-)-LVO group primarily based on catheter angiogram. Procedural and clinical outcomes were compared between the ICAS (+)-LVO and ICAS (-)-LVO groups. Results- The present study included 318 patients. Fifty-six patients (17.6%) had an ICAS (+)-LVO. Recanalization was achieved in 45 patients in the ICAS (+)-LVO group (80.4%), which was comparable with the ICAS (-)-LVO group (88.5%; P=0.097). However, recanalization using a stent retriever was less successful in the ICAS (+)-LVO (28.9%) than the ICAS (-)-LVO group (93.5%). Of the remaining patients in the ICAS (+)-LVO group, 84.3% of patients required specific rescue treatments appropriate for ICAS, including balloon angioplasty, stenting, and intra-arterial glycoprotein IIb/IIIa inhibitor infusion. The rates of favorable outcomes (46.4% versus 46.9%), death, and symptomatic intracranial hemorrhage were not significantly different between the 2 groups. Glycoprotein IIb/IIIa inhibitor use was not significantly associated with symptomatic intracranial hemorrhage. Conclusions- ICAS (+)-LVO was often refractory to mechanical thrombectomy. With specific rescue treatments appropriate for ICAS, patients in the ICAS (+)-LVO group had a recanalization rate comparable with patients in the ICAS (-)-LVO. With comparable recanalization rate, the clinical outcomes did not differ between patients with ICAS (+)-LVO and ICAS (-)-LVO.