Background: The scope of the present study was: to describe the incidence of thromboembolic events (TE) in patients (pts) with resectable oesophagogastric (OG) adenocarcinoma receiving preoperative chemotherapy (CT) with curative intent; to assess risk factors of developing TE; to determine their impact on patient outcome. Methods: Data from 590 pts with OG adenocarcinoma, who received epirubicin, cisplatin and capecitabine (ECX) or 5-fluorouracil (ECF) preoperatively in 3 UK hospitals, between 2009 & 2016, were collected retrospectively. Results: Median age was 66 years (range 28-85), 81% were males, 21% had gastric primaries, 98% received ECX chemotherapy, and 87% completed all 3 cycles of preoperative CT. In total, 52 pts (9%) had a venous and 22 (4%) an arterial event. Of patients with venous TE, 39 had pulmonary embolism and 13 deep vein thrombosis. Of patients with arterial TE, 7 developed cardiac infarct, 8 limb ischemia, 4 cerebrovascular accident and 3 superior mesenteric artery thrombosis. Arterial TE was associated with much higher inoperability rate compared to cases with venous TE or without TE (77% vs. 31% vs. 20% respectively, p < 0.001). Primary tumour location in the stomach (Odds ratio [OR] 3.24, 95%CI 1.72-6.12, p < 0.001), overweight (OR 3.11, 95%CI 1.33-7.26, p = 0.009) or obese status (OR 4.52, 95%CI 1.85-11.09, p = 0.001) and the presence of central venous access (OR 3.40, 95%CI 1.00-11.55, p = 0.050) were independent risk factors for venous TE development, while anticoagulant treatment was independently associated with a lower risk of venous TE (OR 0.22, 95%CI 0.06-0.83, p = 0.026). A very high Khorana score (of 4-5) was the only independent risk factor for arterial TE (OR 6.38, 95%CI 1.85-22.04, p = 0.003). Furthermore, arterial TE was an independent poor prognostic factor for OS when adjusted for baseline patient, tumour and treatment characteristics (Hazard ratio [HR] 3.02, 95%CI 1.85-4.95, p < 0.001). Conclusions: Preoperative ECX/ECF chemotherapy for patients with resectable OG adenocarcinoma was associated with relatively high incidence of TE. However, only arterial TE affected patient outcome Legal entity responsible for the study: Wasat Mansoor Funding: None Disclosure: All authors have declared no conflicts of interest.