Background and Purpose: Cerebral large vessel occlusion (LVO) in acute ischemic stroke (AIS) may be complete (CLVO) or incomplete (ILVO). The influence of ILVO on clinical outcome after mechanical thrombectomy (MT) remains unclear. We investigated primarily the clinical outcome in patients with AIS due to ILVO or CLVO. Methods: Five hundred three consecutive AIS patients with LVO treated with stent-retriever or direct aspiration-based MT between 2010 and 2016 were analyzed. The primary endpoint was favorable clinical outcome (modified Rankin Scale ≤2) at 90 days; secondary endpoints were periprocedural parameters. Results: Forty-nine patients (11.3%) with a median National Institutes of Health Stroke Scale (NIHSS) of 11 presented with ILVO and the remainder presented with CLVO and median NIHSS of 15 (p < 0.001). The median groin puncture-to-reperfusion time was 30 vs. 67 min, respectively (p < 0.001). Successful reperfusion was reached in 47 out of 49 ILVO (95.9%) vs. 298 out of 381 CLVO (78.2%; p < 0.005) with less retrieval maneuvers (1.7 ± 2.2 vs. 3.0 ± 2.5; p < 0.001). The favorable outcome at 90 days was 81% in patients with ILVO vs. 29.1% in CLVO (p < 0.001); respective all-cause mortality rates were 6.4 vs. 28.5% (p < 0.001). Periprocedural complications (6.9%) occurred exclusively in CLVO patients (p < 0.05). ILVO was associated with favorable clinical outcome independent of age and NIHSS in multivariate logistic regression both in the anterior (OR 3.6; 95% CI 1.8-6.9; p < 0.001) and posterior circulation (OR 3.5; 95% CI 1.8-6.9; p < 0.001). Conclusions: AIS due to ILVO is frequent and is associated with a nearly threefold higher chance of favorable clinical outcome at 90 days, independent of age and initial NIHSS compared to CLVO.