Objective <p>This study aims to investigate the association between high-density lipoprotein cholesterol (HDL-C) and diabetic retinopathy (DR) in adults with diabetes, and to explore the mediating role of body roundness index (BRI).</p> Methods <p>In this cross-sectional study, a total of 1658 participants with diabetes from the National Health and Nutrition Examination Survey (NHANES) 2005–2008 were included. This specific period was selected as the first NHANES cycle to systematically include fundus photography for diabetic retinopathy assessment. The diagnosis of DR was based on fundus images evaluated using the Early Treatment Diabetic Retinopathy Study (ETDRS) severity scale. HDL-C levels were measured using Roche Diagnostics. BRI was calculated based on height and waist circumference. Multivariable logistic regression models were used to assess the relationship between HDL-C and DR, and mediation analysis was performed to evaluate the potential mediating effect of BRI.</p> Results <p>The fully adjusted model revealed a significant positive association between HDL-C and DR (OR = 2.08 95% CI: 1.34 ~ 3.22, <i>p</i> = 0.007). In subgroup analyses, positive associations between HDL-C and DR were still observed across various subgroups (including gender, race, smoking status, alcohol use, hypertension history, hyperlipidemia, weight status, and age group). Mediation analysis indicated that BRI played a significant mediating role in the relationship between HDL-C and DR, with a mediation effect of 21.51%.</p> Conclusions <p>Among adults with diabetes in the United States, elevated HDL-C is positively associated with DR, partially mediated through BRI.</p> Clinical trial number <p>Not applicable.</p>