Clinical outcome after mechanical thrombectomy (MT) for large vessel occlusion (LVO) stroke is influenced by the intracerebral collateral status. We tested the hypothesis that patients with preexisting ipsilateral extracranial carotid artery stenosis (CAS) would have a better collateral status compared to non-CAS patients. Additionally, we evaluated MT-related adverse events and outcome for both groups.Over a 7-year period, we identified all consecutive anterior circulation MT patients (excluding extracranial carotid artery occlusion and dissection). Patients were grouped into those with CAS ≥ 50% according to the NASCET criteria and those without significant carotid stenosis (non-CAS). Collateral status was rated on pre-treatment CT- or MR-angiography according to the Tan Score. Furthermore, we assessed postinterventional infarct size, adverse events and functional outcome at 90 days.We studied 281 LVO stroke patients, comprising 46 (16.4%) with underlying CAS ≥ 50%. Compared to non-CAS stroke patients (n = 235), patients with CAS-related stroke more often had favorable collaterals (76.1% vs. 46.0%). Recanalization rates were comparable between both groups. LVO stroke patients with underlying CAS more frequently had adverse events after MT (19.6% vs. 6.4%). Preexisting CAS was an independent predictor for favorable collateral status in multivariable models (Odds ratio: 3.3, p = 0.002), but post-interventional infarct size and functional 90-day outcome were not different between CAS and non-CAS patients.Preexisting CAS ≥ 50% was associated with better collateral status in LVO stroke patients. However, functional 90-day outcome was independent from CAS, which could be related to a higher rate of adverse events.