Background: Duplex ultrasound (DUS) is commonly used to guide pre-operative assessment in diabetic foot ulceration, but its reliability in tibial artery disease remains uncertain. Underestimation of distal disease may affect revascularisation planning. Methods: We performed a retrospective single-centre study of patients with diabetic foot ulceration who underwent ipsilateral lower-limb DUS followed by digital subtraction angiography (DSA) for planned revascularisation. Segment-level DUS findings were compared with DSA for clinically significant disease. Agreement was assessed using observed agreement and Cohen’s kappa. Diagnostic accuracy and predictors of discordance were analysed. Results: A total of 110 patients and 120 limbs were included. Patients were predominantly male (75.5%), with a median age of 69 years; 19.1% had end-stage kidney disease. Agreement between DUS and DSA was highest in the tibioperoneal trunk, superficial femoral artery and popliteal artery, but was only fair in distal tibial vessels, including the anterior tibial, posterior tibial and peroneal arteries. Sensitivity was lowest in the peroneal artery at 46.2%, while specificity was generally high across segments. Multivariable analysis showed that arterial segment, rather than patient-level factors, was the major determinant of discordance. False-negative DUS findings were significantly more likely in the anterior tibial, posterior tibial and peroneal arteries compared with the superficial femoral artery. Conclusion: In patients with diabetic foot ulceration undergoing angiography, DUS demonstrated limited reliability for distal tibial disease and was prone to false-negative findings. These results suggest that DUS may underestimate infrapopliteal disease in limb-salvage populations, supporting a low threshold for angiographic assessment when revascularisation is being considered.