Introduction: Circulating monocyte count is predictive of new atherosclerotic plaque development. In addition, there is a strong inverse relationship between high-density lipoprotein (HDL) cholesterol and atherosclerosis. We aimed to investigate the relationship between the monocyte/HDL cholesterol ratio and severity of coronary artery disease. Patients and Methods: A total of 760 patients who underwent coronary angiography were included in the study. The severity of coronary atherosclerosis was calculated by the Gensini score, and the patients were grouped as having low ( 20) Gensini scores. Baseline characteristics and laboratory parameters were recorded and compared between patients with low and high Gensini scores. Results: Hypertension, diabetes mellitus, hyperlipidaemia, advanced age and smoking were more common in patients with a high Gensini score. Fasting blood glucose levels, creatinine levels and monocyte/HDL cholesterol ratio were significantly lower in patients with a low Gensini score than in those with a high Gensini score. Logistic regression analysis revealed that older age, fasting blood glucose levels, hyperlipidaemia, family history of coronary artery disease and male gender were independent predictors of a high Gensini score. We observed a correlation between the monocyte/HDL cholesterol ratio and Gensini score (p< 0.001). However, this correlation was weak (Spearman’s rho = 0.159). Conclusion: We observed a positive but weak correlation between the monocyte/HDL cholesterol; ratio and increased coronary atherosclerotic burden, as calculated by Gensini scoring. Further studies are required to demonstrate the relationship between the monocyte/HDL cholesterol ratio and atherosclerotic cardiovascular disease.