['To find the associations between diabetic retinopathy and age at diagnosis, C-peptide level and thyroid-stimulating hormone (TSH) level in Chinese type 2 diabetes mellitus.', "3100 hospitalized type 2 diabetic patients in Peking University People's Hospital were included in this retrospective study. Their medical history and the laboratory data were collected. All the patients received examination of diabetic retinopathy (DR) by professional ophthalmologist.", 'Comparisons among patients with NDR, NPDR and PDR showed that with the progression of diabetic retinopathy, patients turned to have older age but younger age at diagnosis of diabetes, and have higher SBP, longer duration of diabetes, higher mean HbA1c but lower fasting and 2 hours postprandial C-peptide level. Moreover, with the progression of diabetic retinopathy, patients turned to have higher prevalence of primary hypertension, higher prevalence of peripheral vascular sclerosis, higher proportion with insulin treatment. TSH level was comparable among the three groups of patients. Association analysis showed that after adjusting for age, sex, duration of diabetes, body mass index, HbA1c, blood pressure and albuminurea creatinine ratio and insulin treatment, age at diagnosis (OR 0.888, 95%CI 0.870-0.907, p\u200a=\u200a0.00) and postprandial C-peptide (OR 0.920, 95%CI 0.859-0.937, p\u200a=\u200a0.00) are the independent associated factors of DR in Chinese type 2 diabetes.'] Are age at diagnosis and C-peptide level associated with diabetic retinopathy in Chinese?