OBJECTIVE: To compare the frequencies of diabetic retinopathy in glaucoma and non glaucoma patients with diabetes mellitus with a view to increasing the body of knowledge of the relationship between glaucoma and diabetic retinopathy. METHODS: The study was a comparative cross sectional study conducted among diabetes mellitus patients with, and without glaucoma, attending the Diabetic Medical Outpatient and Eye clinics of the Lagos University Teaching Hospital, Lagos (LUTH). Ethical approval was obtained from the Health Research and Ethics Committee of Lagos University Teaching Hospital and the tenets of Helsinki were strictly adhered to. Written informed consents were obtained from respondents. Sample size calculation was done using the Kelsey equation for comparative cross-sectional studies. Consecutive consenting diabetic patients with glaucoma, who met the inclusion criteria, were selected as the primary cases for the study. A control group of diabetic patients without glaucoma, matched for age, sex and duration of diabetes mellitus diagnosis, was enrolled. Demographic data was obtained via patient medical records and self administered questionnaires. Respondents received a standardized examination protocol including blood pressure measurement, intraocular pressure measurement, gonioscopy, visual acuity assessment, anterior and posterior segment examinations, blood sample collection and visual field assessment. Outcome measure was the presence and stage of diabetic retinopathy, using the International Diabetic Retinopathy Clinical classification guidelines. Data obtained were analyzed using STATA Version 14 (StataCorp: College Station, TX, USA). Univariate, bivariate and multivariate analyses were carried out and level of significance was taken as less than 0.05 (p<0.05).