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Background Endovascular thrombectomy (EVT) is the standard of care for large vessel occlusion stroke, yet technical failure persists in a significant minority of cases. Intracranial atherosclerotic disease (ICAD) is a recognized driver of failure in Asian populations; its prevalence in Western cohorts is underestimated. We aimed to classify mechanisms of technical failure in a large cohort and investigate the impact of both unrecognized ICAD and anatomical access difficulties.Methods We analyzed 2467 consecutive single-center EVT procedures retrospectively. Failure was defined as final modified Treatment In Cerebral Infarction (mTICI) <2b or no angiographic improvement. Failures were classified into three categories: type 1 (access failure), type 2 (clot accessed but no durable reperfusion), and type 3 (aborted/other). Type 2 failures were adjudicated by consensus to identify features suggestive of ICAD.Results Recanalization failure occurred in 313 patients (12.7%); type 1 accounted for 40 (12.8%), type 2 occurred in 127 (40.6%), and 146 (46.6%) were type 3. Baseline age and stroke severity were similar between successful and failed groups, but failure was associated with significantly longer procedure times (median 60 vs 30 min, P<0.001) and almost threefold higher in-hospital mortality (29.4% vs 11.0%, P<0.001). Among type 2 failures, 18.1% were adjudicated as likely underlying ICAD and 4.7% as possible ICAD. While overall failure rates declined from 23.0% (2012–2015) to 11.2% (2019–2023) driven by improvements in M1 middle cerebral artery recanalization, the incidence of type 1 failures did not significantly improve over time (P=0.20), representing a persistent unmet technical need.Conclusions Despite technical advances, procedural failure remains a distinct event with catastrophic outcomes. Up to 22.8% of retrieval failures in this Western cohort were attributable to likely/possible underlying ICAD rather than refractory emboli.