Objectives: Besides the traditional cardiovascular risk factors, there are numerous anatomical and functional parameters that affect the coronary atherosclerosis and subsequent stenotic coronary artery disease (CAD). Previous studies reported a significant association between coronary artery diameter and stenotic CAD. However, no study has investigated the association between the ratio of ostial diameter of the main coronary arteries and stenotic CAD. We aimed to investigate whether coronary artery ostial diameter ratio (CAOD-R), which is calculated as dividing the left main coronary artery (LMCA) ostial diameter by the right coronary artery (RCA) ostial diameter, was associated with the presence of stenotic CAD in patients undergoing elective coronary angiography. Materials and Methods: Four hundred and thirty-six patients who underwent elective coronary angiography were included in the study. CAOD-R was calculated from digital angiograms for all patients, and patients were divided into two groups as CAOD-R [less than or equal to] 1or 1. The groups were compared regarding the frequency of patients with stenotic CAD, and the association of CAOD-R with the presence of stenotic CAD was investigated. Results: According to calculated CAOD-R, 142 (32.6%) patients were in the CAOD-R [less than or equal to]1 group and 294 (67.4%) patients were in the CAOD-R 1 group. Patients with CAOD-R 1 (61.9% vs 41.1%, p 1 patient group (28.9% vs 18.2%, p=0.002). There were no differences between the groups regarding the frequency of stenotic lesions in LMCA and left circumflex artery. Furthermore, multivariate analysis demonstrated that CAOD-R was an independent predictor of stenotic CAD (Odds ratio: 0.824, 95% confidence interval: 0.721-0.947, p Conclusion: The present study demonstrated that CAOD-R was an independent predictor of stenotic CAD in patients undergoing elective coronary angiography. As an easily calculated parameter from angiographic images, CAOD-R may be useful in the further risk assessment of CAD patients undergoing elective coronary angiography. Keywords: Coronary artery disease, coronary artery diameter, coronary angiography, coronary artery ostial diameter ratio