<h3>Study Objective</h3> Determine effect of length of surgery (LOS) on risk for venous thromboembolism (VTE) after hysterectomy and determine if differences exist based on age, body mass index (BMI), and surgical approach. <h3>Design</h3> Secondary analysis of prospectively-collected surgical quality improvement data. <h3>Setting</h3> American College of Surgeons National Surgical Quality Improvement Program database, containing demographic, perioperative information and 30-day postoperative outcomes from >500 hospitals, and targeted data files including procedure-specific risk factors and outcomes for a subset of hospitals. <h3>Patients or Participants</h3> Patients undergoing abdominal (AH), vaginal (VH), or laparoscopic hysterectomy (LH), identified with Current Procedural Terminology (CPT) codes, for benign indications from 2014-2016 were eligible. Patients with cancer, surgery not performed by a gynecologist, not in targeted files, missing LOS, or LOS <30 minutes were excluded. <h3>Interventions</h3> Patients were compared with respect to incidence of VTE and LOS, stratified by age, BMI, and surgical approach. <h3>Measurements and Main Results</h3> 48,813 patients were included. VTE incidence was 0.3%. Patients with VTE were obese, had greater uterine weight, and had inpatient procedures. Multivariable logistic regression was performed; LOS was treated as a continuous variable. Adjusting for confounders, for each 60 minute increase in LOS, there was a 41% increase in odds of VTE. Stratified by surgical approach, odds of VTE per 60 minute increase in LOS were greatest after AH (aOR 1.56, 95%CI 1.4, 1.75) compared to LH (aOR 1.19, 95%CI 0.76, 1.85) and VH (aOR 1.24, 95%CI 1.04, 1.47). As BMI increased, odds of VTE per 60 minutes increased: <30kg/m<sup>2</sup> (aOR 1.31, 95%CI 1.11, 1.55), 30-39kg/m<sup>2</sup> (aOR 1.43, 95%CI 1.24, 1.65), and ≥40kg/m<sup>2</sup> (aOR 1.46, 95%CI 1.23, 1.72). There was no modification of risk by age. <h3>Conclusion</h3> Our study suggests given the increased odds of VTE per 60 minute increase in LOS, the risk of VTE is cumulative. Prolonged LOS or obese patients may benefit from pharmacological and mechanical prophylaxis.