Introduction: Kidney dysfunction (KD) is a risk factor for cerebrovascular events and has been shown to have a detrimental effect on outcome after stroke. We evaluated the influence of KD at admission and pre-existing diagnosis of chronic kidney disease (CKD) before thrombectomy for anterior circulation stroke on functional independence and mortality 90 days after stroke in this cross-sectional study. Patients and methods: We included patients with acute ischemic stroke in the anterior circulation treated with thrombectomy at our hospital between June 2015 and May 2022. We analyzed clinical characteristics, laboratory values and pre-existing diagnosis of CKD. KD at admission was defined as glomerular filtration rate (GFR) <60 ml/min/1.73 m². Outcomes were defined as a modified Rankin Scale Score of 0-2 for functional independence and mortality at 90 days. We fitted multivariate regression analysis to examine the influence of pre-treatment KD and pre-diagnosed CKD on outcome. Results: Nine hundred fifty-three patients were included in this analysis (mean age 73.8 years, 54.2% female). KD was present in 31.8%, and patients with KD were older and more often female, presented more often with comorbidities such as arterial hypertension, diabetes, and atrial fibrillation, and were less often independent before the index stroke. In multivariate analysis adjusted for age, independence before the index stroke, diabetes, hypertension, atrial fibrillation, initial NIHSS, thrombolysis treatment, and recanalization outcome, KD on admission had no significant influence on functional independence 90 days after stroke, but predicted mortality with an odds ratio of 1.80 (95% CI 1.23–2.63, p = 0.003). This influence also persisted when controlling for pre-diagnosed CKD (OR 1.60, 95% CI 1.05–2.43, p = 0.027). Discussion: KD might function as a surrogate parameter for comorbidity burden and thus increased risk of mortality in this cohort. Conclusions: KD on admission is associated with an 80% higher risk of mortality at 90 days after stroke thrombectomy independent of cardiovascular risk factors and CKD awareness. KD on admission should not exclude patients from thrombectomy but might support prognostic evaluation.