Introduction: Even with reperfusion therapies, the prognosis of patients with basilar artery occlusion (BAO) related stroke remains poor. We aimed to test the hypothesis that the presence of prodromal symptoms, an easily available anamnestic data, is a key determinant of poor functional outcome. Patients and methods: Data from patients with BAO treated in Lille, France, with mechanical thrombectomy (MT) between 2015 and 2021 were prospectively collected. The presence of prodromal symptoms was defined by previous transient neurological deficit or gradual progressive clinical worsening preceding a secondary sudden clinical worsening. We compared the characteristics of patients with and without prodromal symptoms. We built multivariate logistic regression models to study the association between the presence of prodromal symptoms and functional (mRS 0–3 and mortality), and procedural (successful recanalization and early reocclusion) outcomes. Results: Among the 180 patients, 63 (35%) had prodromal symptoms, most frequently a vertigo. Large artery atherosclerosis was the predominant cause of stroke (41.3%). The presence of prodromal symptoms was an independent predictor of worse 90-day functional outcome (mRS 0–3: 25.4% vs 47.0%, odds ratio (OR) 0.39; 95% confidence interval (CI) 0.16–0.86) and 90-day mortality (OR 2.17; 95% CI 1.02–4.65). Despite similar successful recanalization rate, the proportion of early basilar artery reocclusion was higher in patients with prodromal symptoms (23.8% vs 5.6%, p = 0.002). Discussion and conclusion: More than one third of BAO patients treated with MT had prodromal symptoms, especially patients with large-artery atherosclerosis. Clinicians should systematically screen for prodromal symptoms given the poor related functional outcome and increased risk of early basilar artery reocclusion.