Purpose: To compare optical coherence tomography angiography (OCTA) findings between severe non-proliferative diabetic retinopathy (NPDR) and unexposed proliferative diabetic retinopathy (PDR), and identify predictive factors. Methods: Patients newly diagnosed with severe NPDR or unexposed PDR between January 2018 and December 2021 were reviewed retrospectively. Unexposed PDR was diagnosed using fluorescein fundus angiography, because new vessels could not be observed in the poster pole or clearly distinguished in the retinal periphery on wide fundus photography. Clinical features at the time of diagnosis, and OCTA measurements (mean vascular density, superficial capillary plexus (SCP) foveal avascular zone (FAZ) area, and mean retinal thickness), were compared between the two groups. Factors that could predict unexposed PDR were investigated using multivariate analysis with a generalized estimating equation. Results: A total of 61 severe NPDR and 23 unexposed PDR eyes were included. The unexposed PDR had significantly larger SCP-FAZ areas (p = 0.031) and lower total and parafoveal mean inner retinal thicknesses (p = 0.014 and p < 0.001, respectively). However, there were no differences in mean vascular density between the groups (p > 0.05). Multivariate analysis showed that SCP-FAZ area and parafoveal mean inner retinal thickness were significant predictors of unexposed PDR (p = 0.027 and p = 0.001, respectively). Conclusions In severe NPDR patients, unexposed PDR may be considered a differential diagnosis when the SCP-FAZ area is large or the parafoveal mean inner retinal thickness is small.