To investigate the association between retinal vascular tortuosity and traditional- and vascular-related risk factors in persons with diabetes.We recruited 224 diabetic patients. Retinal vascular tortuosity was measured from fundus photographs. Association of tortuosity with the following factors was assessed after adjusting for significant co-factors: diabetes duration, HbA1c, systolic blood pressure (SBP), cholesterol and body mass index (BMI), flicker-light induced retinal vasodilatation, and markers of endothelial function and inflammation (skin microvacular responses to acetylcholine iontophoresis, soluble e-selectin, inter-cellular adhesion molecule-1, vascular cell adhesion molecule-1, endothelin-1, total nitrite, C-reactive protein).Adjusting for age and gender, longer diabetes duration was associated with more tortuous retinal arterioles (mean difference in arteriolar tortuosity 5.85 × 10(-5), 95% Confidence Interval 1.44-10.3 × 10(-5); p = 0.016; ≤10 versus >10 years duration). Reduced flicker-light induced retinal vasodilatation was associated with tortuous arterioles and venules (mean difference in arteriolar tortuosity 5.62 × 10(-5), 4.50-6.72 × 10(-5); p < 0.001 and in venules 5.94 × 10(-5), 3.33-8.55 × 10(-5); p < 0.001; comparing highest versus lowest tertile of flicker-light vasodilatation). These associations remained after adjusting for co-factors. Diabetes duration explained about 36% and flicker-light vasodilatation 25% of the variation in retinal arteriolar tortuosity. No associations were found between retinal arteriolar or venular tortuosity and HBA1c, SBP, cholesterol, BMI and serum markers of endothelial function.Increased retinal arteriolar tortuosity was related to longer diabetes duration and reduced flicker-light induced vasodilatory response, suggesting that retinal vascular tortuosity in adults with diabetes may be influenced by multiple diabetes-related physio-pathological changes.