Background: Venous thromboembolism (VTE) causes significant morbidity and mortality in patients with cancer. The International Society of Thrombosis and Hemostasis published guidelines in 2014 recommending a risk-based approach to VTE prophylaxis in ambulatory cancer patients, but uptake in real-world clinical practice is unknown. This study's objective was to describe rates of primary VTE prophylaxis in ambulatory patients with gastric and pancreatic cancer receiving chemotherapy and at increased risk of VTE. Methods: We identified patients at a single academic tertiary care center who received chemotherapy from 1/1/2015 to 10/1/2018 for a diagnosis of pancreatic or gastric cancer through retrospective query of electronic health records. Data abstracted included the Khorana score components (body mass index, leukocyte, hemoglobin, and platelet counts) on day of chemotherapy initiation, anticoagulation prescription, and VTE diagnosis within 6 months of chemotherapy initiation. Patients were excluded if they had contraindications to anticoagulation or alternate indications for anticoagulation. Results: We identified 437 patients, of which 72% had pancreatic cancer and 29% had gastric cancer. Mean (standard deviation) age was 64.2 (11.7) years, and patients were predominately male (54%) and white (75%). Overall, only 13% of patients received a prescription for anticoagulation with similar rates in patients with pancreatic cancer (14%) compared to gastric cancer (9%). Anticoagulation prescription rates by Khorana score (2 or ≥3) are shown in Table. Approximately 10% of patients had a VTE within 6 months of chemotherapy initiation. Conclusions: Our results show that in a cohort of patients with gastric and pancreatic cancer at intermediate to high-risk of VTE by Khorana score (≥2), only 1 in 10 received a prescription for prophylactic anticoagulation. In addition, we observed high rates of incident VTE in 6-month follow-up confirming the high-risk nature of this group. Opportunity remains to enhance implementation of primary VTE prevention in clinical practice to reduce VTE morbidity and mortality in patients with cancer.