INTRODUCTION: The pathophysiology of microvascular disease is poorly understood, partly due to the lack of tools to directly image microvessels in vivo. RESEARCH DESIGN AND METHODS: In this study, we deployed a novel optical coherence tomography (OCT) technique during local skin heating to assess microvascular structure and function in diabetics with (DFU group, n=13) and without (DNU group, n=10) foot ulceration, and healthy controls (CON group, n=13). OCT images were obtained from the dorsal foot, at baseline (33°C) and 30 min following skin heating. RESULTS: At baseline, microvascular density was higher in DFU compared with CON (21.9%±11.5% vs 14.3%±5.6%, p=0.048). Local heating induced significant increases in diameter, speed, flow rate and density in all groups (all p<0.001), with smaller changes in diameter for the DFU group (94.3±13.4 µm), compared with CON group (115.5±11.7 µm, p<0.001) and DNU group (106.7±12.1 µm, p=0.014). Heating-induced flow rate was lower in the DFU group (584.3±217.0 pL/s) compared with the CON group (908.8±228.2 pL/s, p<0.001) and DNU group (768.8±198.4 pL/s, p=0.014), with changes in density also lower in the DFU group than CON group (44.7%±15.0% vs 56.5%±9.1%, p=0.005). CONCLUSIONS: This proof of principle study indicates that it is feasible to directly visualize and quantify microvascular function in people with diabetes; and distinguish microvascular disease severity between patients.