BACKGROUND: Approximately half of patients who achieve successful reperfusion do not achieve functional independence. The present study sought to investigate the clinical outcomes and safety of intraarterial or intravenous tirofiban as adjunct therapy in patients with acute basilar artery occlusion who had achieved successful recanalization with endovascular treatment. METHODS AND RESULTS: In the national, prospective BASILAR (Endovascular Treatment for Acute Basilar Artery Occlusion Study) registry, 458 patients who met inclusion criteria were divided into 3 groups based on tirofiban administration (no tirofiban, n=262; intravenous tirofiban, n=101; intraarterial+intravenous tirofiban, n=95). Their clinical outcomes were compared with 90-day modified Rankin Scale scores. Adjusted odds ratios (aORs) and 95% CIs were obtained by logistic regression models and propensity score matching. Safety outcomes included any intracranial hemorrhage (ICH), symptomatic ICH, and mortality. Among 458 included patients, 184 (40.2%) achieved a favorable outcome (modified Rankin Scale score 0-3). There were no differences between the intravenous tirofiban group and the no tirofiban group in terms of safety and clinical outcomes (all P>0.05). Compared with the no tirofiban group, the intraarterial+intravenous tirofiban group had higher odds of 90-day modified Rankin Scale score 0 to 3 (aOR, 2.44 [95% CI, 1.30-4.64], P=0.006) and lower 3-month mortality (aOR, 0.38 [95% CI, 0.19-0.71], P=0.002) without an increase in any ICH (aOR, 0.34 [95% CI, 0.09-1.01], P=0.07) or symptomatic ICH (aOR, 0.23 [95% CI, 0.03-0.90], P=0.05). Similar results of intraarterial+intravenous tirofiban on improving clinical outcomes were detected in novel cohorts constructed by propensity score matching. CONCLUSIONS: Intraarterial+intravenous rather than intravenous tirofiban improved clinical outcomes without increasing the frequency of symptomatic ICH among patients with basilar artery occlusion after successful endovascular treatment. Further studies are needed to delineate the roles of intraarterial+intravenous tirofiban in patients with basilar artery occlusion receiving endovascular treatment.