BACKGROUND Diabetes mellitus is a chronic degenerative systemic disease whose prevalence is increasing. This paper aims to evaluate the effects of diabetic microangiopathy, depending on its duration and the type of treatment administered, by using polarized light videocapillaroscopy of the oral mucosa. MATERIAL AND METHODS We enrolled 120 subjects: 60 healthy subjects and 60 patients with diabetes mellitus. In turn, patients were divided into 3 subgroups according to the type of diabetes, the duration of the disease, and the type of treatment administered. A videocapillaroscopic examination of the oral mucosa was carried out on the diabetic and healthy subjects. RESULTS Changes in microcirculation were detected in diabetic patients: at the level of the labial, buccal, and lingual mucosa, the density of the loops is on average reduced; there is an increase in the length and the total diameter of the loops, while the average density of the periodontal capillaries is much higher. The most significant changes were noted in patients who had had type 1 diabetes for more than 10 years and had received insulin therapy. CONCLUSIONS This study, performed using polarized light videocapillaroscopy, which for the first time was used to analyze the capillaries of the oral mucosa in patients with diabetes, confirms the presence of changes that are instrumentally "objectifiable" and "quantifiable" through the videocapillaroscopic technique. Videocapillaroscopy can be a reliable method in the study and monitoring of complications in patients with type 1 and 2 diabetes mellitus.