Purpose: The aim of this study was to assess longitudinal changes in retinal vessel density in diabetic patients using optical coherence tomography angiography (OCTA) to identify the most sensitive parameter for detecting retinopathy progression. Methods: Patients with diabetes mellitus were enrolled in this study. Each study subject underwent two imaging sessions, during which three OCTA images of the macular area and three images of the optic nerve head were obtained. The two sessions took place one year apart. The OCTA imaging was performed using an AngioVue device. Superficial vessel density was evaluated in the central 3mm and parafoveal area, and the nonflow area was measured using the built-in automated AngioAnalytics software of the Optovue system. Results: This study included 78 eyes of 39 diabetic patients (age: 55.16 +- 13.73 years) with a mean of 7.70 +- 1.07mmol L-1 HgA1c level at baseline. At the one-year visit, the eyes of the diabetic subjects had significantly lower superficial vessel density in the parafoveal macula compared to corresponding values at baseline (p < 0.05). There was no statistically significant difference between the baseline and one-year results for the other vascular density parameters and the foveal avascular zone (p > 0.05). Conclusion: At the one-year follow-up, we found that vessel density had decreased in the parafoveal ring in these patients, while there was no significant change in other vascular parameters. This result suggests that superficial parafoveal capillary density is the most sensitive OCTA parameter that can be used as a biomarker for diabetic retinopathy progression. None of the other vascular density parameters nor the foveal avascular zone were able to indicate the subtle changes in retinal microcirculation due to the progression of diabetic microvasculopathy.  Kulcsszavak: OCT angiography, diabetic retinopathy