Diabetic retinopathy (DR) is a common microvascular complication of diabetes, and identifying the risk factors for severe DR is important. We aimed to investigate the relationship between severe DR and the extracellular water to total body water ratio (ET ratio). Retrospective cross-sectional study. Department of Endocrinology, Metabolism, and Diabetes at Kyushu University Hospital. A total of 205 adults with type 2 diabetes (T2D) were included. The patients were divided into two groups: non-proliferative DR (non-PDR; n = 161, 126 with no DR and 35 with simple DR) and proliferative DR (PDR; n = 44, 18 with pre-proliferative DR and 26 with PDR). The ET ratio was measured using bioelectrical impedance analysis. The ET ratio was significantly higher in the PDR group than in the non-PDR group (0.390 vs. 0.398; P < .0001). Multivariate logistic regression analysis showed that the ET ratio was significantly associated with PDR, independent of known risk factors for DR progression. In the subgroup analysis by age, multivariate logistic regression analysis revealed a significant association between the ET ratio and PDR, independent of known risk factors for DR progression in patients younger than 60 years. However, in patients 60 years and older, only the urinary albumin to creatinine ratio (UACR) showed a significant association with PDR in a model using the UACR and the ET ratio. In patients with T2D younger than 60 years, the ET ratio may be a useful indicator for identifying severe DR.