BACKGROUND : The aim of this study was to evaluate the relationship between the choroidal structure of diabetic patients without diabetic retinopathy (DR) and duration of diabetes. METHODS : This study is a retrospective observational study in diabetic patients without DR. Eyes with diabetes mellitus (DM) (n = 105) were divided into two groups based on the duration: long duration group (over 10 years, n = 31) and short duration group (less than 10 years, n = 74). One hundred seventeen eyes of non-diabetic patients were used as control group. All patients underwent enhanced depth imaging optical coherence tomography, and the choroidal structure was analyzed using a binarization method. RESULTS : There was no significant difference in areas of total choroid and lumina/stroma or central choroidal thickness (CCT) between control and DM groups. In contrast, lumina/total choroidal (L/C) ratio was significantly lower in diabetic eyes than in control eyes (P = 0.02). Although there was no significant difference in the areas or CCT between short and long duration groups, L/C ratio was significantly lower in the long duration group than in the short duration group (P = 0.03). CONCLUSIONS : The current study suggests that choroidal vasculature is involved in the diabetic eyes and that the choroidal structure has changed with duration of diabetes. Our study points out that L/C ratio is a new potential biomarker in monitoring choroidal vascular disorders in diabetic eyes without DR.