Purpose To assess ocular and systemic factors associated with diabetes mellitus in the adult population in rural and urban China. Methods The Beijing Eye Study 2006, a population-based, cross-sectional cohort study, included 3251 subjects aged 45 years and more (participation rate: 73.2%). Blood samples were available for 2960 (91.0%) subjects. Diabetes mellitus was defined by a fasting plasma glucose concentration >= 7.0 mmol/l or by a self-reported history diagnosis of diabetes. Results Diabetes mellitus was found in 381 (12.9%) subjects. In binary regression analysis, the presence of diabetes mellitus was significantly associated with body mass index, systolic blood pressure, triglyceride concentrations, intraocular pressure, cylindrical refractive dioptre, presence of arteriolar sheathing, rural vs urban region, lower best-corrected visual acuity, lower highdensity lipoprotein level, and lower diastolic blood pressure. It was not statistically associated with age, presence of cataract (nuclear, cortical, or subcapsular), size of the optic disc, neuroretinal rim, a zone and beta zone of peripapillary atrophy, retinal artery and vein diameters, arteriovenous nicking, focal or general narrowing, refractive error, prevalence of glaucoma, and early or late stage of age-related macular degeneration. Conclusions In a population-based setting, diabetes mellitus was not associated with optic disc, rim and peripapillary atrophy measurements, retinal vessel diameters, arteriovenous nicking, focal or general retinal artery narrowing, and prevalence of age-related macular degeneration. Although diabetes mellitus was significantly correlated with higher intraocular pressure, it was not associated with glaucoma.