Background: Although coiling with a flow diverter may provide immediate dome protection, no studies have evaluated the effect on complications of postoperative occlusion degree immediately postoperatively. The purpose of this study was to determine whether postoperative occlusion degree immediately after flow-diverter placement with adjunctive coiling was associated with complications. Methods: All patients' data were collected from the post-market multi-center cohort study of embolization of intracranial aneurysms with a pipeline embolization device (PED) in China (PLUS) registry. We divided patients into those treated with a PED alone (PED-only (PO) group), those treated with a PED with coils and incomplete occlusion (PED + coils + incomplete occlusion (PCIO) group), and those treated with a PED with coils and complete occlusion (PED + coils + complete occlusion (PCCO) group). Results: We evaluated 1171 consecutive patients with 1322 aneurysms treated with a PED: 685 aneurysms were treated with PO, 444 with PCIO, and 193 with PCCO. The PCCO group had a higher rate of aneurysm occlusion at the last follow-up than the PCIO and PO groups (P<0.0001). Multivariate analysis of the predictors of ischemic stroke and modified Rankin Scale score (mRS) deterioration showed that PCCO was an independent predictor of ischemic stroke (HR, 2.03; 95% CI, 1.12 to 3.67; P=0.019) and mRS deterioration (HR, 2.59; 95% CI, 1.57 to 4.26; P<0.0001). Conclusions: Although postoperative complete occlusion with a PED and adjunctive coiling can increase the rate of aneurysm occlusion, this approach may also increase the risk of ischemic stroke and lead to poor postoperative functional outcomes. © Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.