Background: To evaluate systematic duplex ultrasound (DUS) surveillance of patients treated with in situ great saphenous vein bypass (ISSVB) due to critical limb-threatening ischemia (CLTI) we performed a retrospective analysis of prospectively entered registry data. Methods: Single-center study including consecutive patients undergoing elective ISSVB surgery due to CLTI between 2011 and 2015. Postoperative graft surveillance program included clinical examination, ankle-brachial indices (ABIs), and DUS at 6 weeks and 3 and 12 months. All DUS scans were performed by trained nurse sonographers. Patient data were extracted from the Danish Vascular Registry, electronic medical records and Picture Archiving and Communication System (PACS). Primary outcomes were reintervention rate, patency, and survival. Results: In total, 363 consecutive and treatment-naive CLTI patients were revascularized with ISSVB and included in the study. Of those, 310 patients had minimum one follow-up visit and in total 1,199 DUS examinations. During the study period, 84 (23%) patients received 125 graft preserving reinterventions of which 20 were indicated solely on routine DUS without concurrent ischemic symptoms and/or significant (>15%) decrease in ABI. Hence, to find one asymptomatic graft stenosis requiring reintervention, we needed to scan 60 patients. After 1, 2, and 3 years, assisted primary patency was (Kaplan-Meier estimate) 79.4% (95% CI: 74.4, 83.5), 76.3% (95% CI: 70.7, 81.0), and 73.6% (95% CI: 66.9, 79.2), respectively. Survival rates were 82.6% (95% CI: 78.1, 86.3), 64.2% (95% CI: 57.8, 69.9) and 47.7% (95% CI: 40.6, 54.4) at 1, 2, and 3 years, respectively. Conclusions: In this study, one in four patients received a graft preserving intervention, but very few were driven by routine DUS and most graft lesions were detected on clinical findings. These findings suggest that development of a more individualized surveillance program differentiating between high- and low-risk infrainguinal bypass patients may increase cost-effectiveness.