Background: Obesity is a well-established risk factor for venous thromboembolic events, such as pulmonary emoblism and deep vein thrombosis. The rising prevalence of obesity and its associated co-morbidities, including VTE, represent a growing public health issue. Bariatric surgery has been widely validated as an effective method of achieving weight reduction in patients with obesity. However, the impact of this weight loss on the long-term risk of thromboembolic events has yet to be explored. The aim of the present study is to evaluate the effect of bariatric surgery on long-term risk of venous thromboembolic events in a large cohort of patients with obesity. Methods: A nested cohort study was designed; including the 4,056 patients of the Clinical Practice Research Datalink database who had undergone bariatric surgery, and equal numbers of age, gender and BMI matched controls. The primary endpoint of the study was the occurrence of any venous thromboembolic event; with secondary endpoints of deep vein thrombosis alone, pulmonary embolism alone and all-cause mortality. A landmark analysis was carried out to describe and quantify the time-dependent pattern of thromboembolic risk in the initial three years following bariatric surgery. Data was analysed using a Cox proportional hazards model accounting for multiple covariates. Results: Patients were followed up for a median of 10·7 years. The bariatric surgery cohort had a significantly lower occurrence of the primary outcome (HR 0·601; 95%CI 0·430-0·841, p=0·003); mainly driven by a reduction in deep vein thrombosis (HR 0·523; 95% CI 0·349-0·783, p=0·002) and not in pumonary embolism (HR 0·882; 95% CI 0·511-1.521, p=0·651). Conclusion: The results of this nation-wide investigation set out to characterise the impact of bariatric surgery on long-term risk of thromboembolic events in patients with obesity outline a significant reduction in thromboembolic events, driven by a reduction in deep vein thrombosis only.