Background Venous thromboembolism (VTE) is a preventable cause of morbidity and mortality. Emergency general surgery (EGS) patients comprise 7% of hospital admissions in America with a reported rate of VTE of 2.5%. Of these, >69% required hospital readmission, making VTE the second most common cause for readmission after infection in EGS patients. We hypothesize a correlation between body mass index (BMI) and VTE in EGS patients. Methods The American College of Surgeons National Surgery Quality Improvement Database (NSQIP) was queried from January 2015 to December 2016. 83 272 patients met inclusion criteria: age ≥18 and underwent an EGS procedure. Patients were stratified by BMI. Descriptive statistics were used for demographic and numerical data. Categorical comparisons between covariates were completed using the chi-square test. Continuous variables were compared using Student’s t-test, Mann Whitney U-test, or Kruskal-Wallis H test. Results 83 272 patients met the inclusion criteria. 1358 patients developed VTE (903 deep vein thrombosis (DVT) only, 335 pulmonary embolism (PE) only, and 120 with DVT and PE). Morbidly obese patients were 1.7 times more likely to be diagnosed with a PE compared with normal BMI ( P = .004). Increased BMI was associated with the co-diagnosis of PE and DVT ( P = .027). Patients with BMI <18.5 were 1.4 times more likely to experience a VTE compared with normal BMI ( P = .018). Patients with a VTE were 3.2 times more likely to die ( P < .001) and less likely to be discharged home ( P < .001). Discussion Our study found that obese and underweight EGS patients had an increased incidence of VTE. Risk recognition and chemoprophylaxis may improve outcomes in this population.