Purpose: to describe the occurrence of branch thrombosis following endovascular treatment of aortic arch pathology using an arch branched device (ABD) and to determine whether this is influenced by clinical and geometric parameters. Methodology: in this retrospective observational multi-centre study the primary endpoint was thrombus formation within a branch. Secondary endpoints were technical success, serious adverse events, early and late death, stroke, and re-interventions. Geometric measurements (tortuosity index and curvature) were determined on pre- and post-operative CT angiograms. Results: 39 patients were treated and 68 antegrade branches analysed. Thrombus was identified within 7 branches (10%) and was associated with a wider distal bridging stent diameter (median 14.0 mm [13.3, 15.3] vs. 8.7 mm [IQR 5.9]; p ¼ .026), a higher degree of reversed tapering (4.3 mm [3.8, 5.2] vs. 1.2 mm [0.3, 3.1]; p ¼ .023), use of polyethylene terephthalate (Dacron) covered (vs. expanded polytetrafluoroethylene) bridging stents (23% vs. 2%; p ¼ .011), and higher body mass index (BMI) (32.1 kg/m2 [28.7, 36.2] vs. 25.7 kg/m2 [23.8, 29.2]; p ¼ .029), but not with pre- or post-operative tortuosity index or curvature or alterations. Technical success rate was 97%, SAEs occurred in 15 patients (38%), early and late death rates were 8% and 23% and early and late stroke rates were 5% and 23%. Conclusion: The risk of developing branch thrombosis with an ABD is considerable, especially of innominate artery branches, characterised by Dacron covered large diameter bridging stents, and in patients with a high BMI.