AIM: To investigate foveal avascular zone (FAZ) and parafoveal vessel densities (PRVD) by means of optical coherence tomography angiography (OCTA) in diabetic patients with or without diabetic retinopathy (DR) and to assess the reproducibility of FAZ and PRVD measurements. METHODS: Sixty diabetic patients (60 eyes) with different stage of DR (graded according to the International Clinical Severity Scale for DR) and 20 healthy subjects underwent FAZ area and PRVD measurements using OCTA by two experienced examiners. FAZ area in all patients was also assessed using fluorescein angiography (FA). RESULTS: In subject with proliferative DR and with moderate-severe non proliferative DR, FAZ area was significantly increased compared to healthy controls (P=0.025 and P=0.050 respectively measured with OCTA and P=0.025 and P=0.048 respectively measured with FA). OCTA showed significantly less inter-observer variability compared to FA. Concordance correlation coefficient (CCC) for FAZ area measurements was 0.829 (95%CI: 0.736-0.891) P<0.001 with FA and 1.000 (95%CI: 0.999-1.000) P<0.001 with OCTA. CCC was 0.834 (95%CI: 0.746-0.893) P<0.001 and 0.890 (95%CI: 0.828-0.930) P<0.001 for parafoveal superficial and deep vessel density measurements, respectively. CONCLUSION: OCTA shows progressive increase of FAZ area and reduction of PRVD in both superficial and deep plexus at increasing DR severity. FAZ area and PRVD measurements using OCTA are highly reproducible.