Background and Purpose— In middle cerebral artery occlusion, probability of recanalization after intravenous tissue-type plasminogen activator thrombolysis (IVT) was reported to drop <1% for thrombi exceeding 8 mm. We aimed to evaluate the effect of thrombus length and location on success of recanalization after IVT in basilar artery occlusion. Methods— We evaluated 164 consecutive patients with angiography-proven basilar artery occlusion and available thrombus length. We excluded 24 patients who underwent endovascular treatment. All included patients (n=140) received IVT. Thrombolysis in myocardial infarction 2 to 3 was considered as successful recanalization. Results— Of the 140 included patients, 37 (26.4%) lacked post-treatment angiography, mostly because of early death. Of the remaining 103 patients, those with recanalization had shorter thrombi (median, 5.5 mm and mean, 9.7 mm) when compared with those with nonrecanalized (median, 15.0 mm and mean, 16.6 mm; P <0.001). Thrombi shorter than 10 mm had 70% to 80% probability of recanalization, whereas 10 to 20 mm, 20 to 30 mm, and >30 mm long thrombi had probabilities of 50% to 70%, 30% to 50%, and 20% to 30%, respectively. Patients with thrombi <10 mm (n=52) and recanalization had more frequently top-of-the basilar (92.5%) and less frequently caudal or midbasilar (7.5%) clot location ( P =0.01). In multivariable analysis, thrombus length was independently associated with recanalization ( P =0.001). Their relationship remained linear across all lengths. Conclusions— Although recanalization of basilar artery occlusion with IVT depends on thrombus length, its probability even in patients with thrombi >30 mm (20%–30%) was substantially higher than minimal recanalization of middle cerebral artery thrombi exceeding 8 mm. There was no threshold length, beyond which basilar artery occlusion recanalization with IVT could ad hoc be deemed hopeless.