Abstract Introduction Admission hyperglycemia and high admission blood glucose levels have been associated with poor outcomes in acute ischemic stroke. However, the relationship between admission hyperglycemia and outcomes after endovascular treatment (EVT) in acute basilar artery occlusion (ABAO) still remain unclear. This study aimed to investigate the association between admission hyperglycemia and clinical outcomes in ABAO following EVT. Methods Patients from the BASILAR registry with admission blood glucose levels treated with EVT were included. We defined admission hyperglycemia as blood glucose levels ≥ 7.8 mmol/L. The primary outcome was favorable outcome [defined as a modified Rankin Scale score (mRS) of 0–3] at 90 days, Secondary outcomes included other functional outcomes (mRS 0–2, mRS 0–1) at 90 days, symptomatic intracerebral hemorrhage (sICH) within 48 h, and mortality at 90 days. Results Of 545 eligible patients included, the median age was 65 (IQR, 56–73) years, and median blood glucose level was 7.36 (IQR, 6.10–9.66) mmol/L. Multivariable logistic regression analysis showed that admission hyperglycemia was associated with decreased favorable outcome (mRS 0–3) (adjusted odds ratio = 0.52; 95% CI 0.35–0.79; P = 0.001), and increased mortality (adjusted odds ratio = 2.67; 95% CI 1.82–3.91; P