Recently, the monocyte count to high-density lipoprotein cholesterol ratio (MHR) was found to be associated with the SYNTAX score in patients with both stable coronary artery disease (CAD) and acute coronary syndrome (ACS). The MHR was significantly higher in male patients. However, the sex-specific association of MHR with SYNTAX score in stable CAD was not well explored. Thus, the present study aimed to investigate the association of MHR and presence and severity of CAD evaluated by coronary angiography and the SYNTAX score in males and females.In total, 873 patients who received selective coronary angiography between March 2017 and July 2018 were included in the present study. Patients were divided into 3 groups according to MHR tertiles. The MHR was calculated by dividing the monocyte count by the high-density lipoprotein cholesterol level. CAD was defined as at least 50% diameter stenosis of a major coronary artery, including the right coronary, left main coronary, left anterior descending, and left circumflex arteries. The SYNTAX score was calculated by 2 experienced interventional cardiologists. SYNTAX score ≥23 was defined as a high SYNTAX score.Males showed a significantly higher MHR (12.2 [8.9-15.5] vs 9.3 [6.2-12.1], P < .001), accompanied by a higher prevalence of CAD (68.1% vs 53.4%, P < .001). Male sex remained an independent predictor of elevated MHR after correction for confounding factors (adjusted odds ratio [OR] 3.102, P = .001). The association between MHR and SYNTAX score was confirmed only in male stable patients with CAD (r = 0.113, P = .036). Multivariate logistic regression analysis showed that MHR was an independent predictor of SYNTAX score ≥23 only in male patients with CAD. The receiver-operating characteristic curve showed a predictive value of MHR for high SYNTAX score only in males.A higher MHR in males and a positive correlation of MHR with SYNTAX score were observed only in male stable patients with CAD. Such an easily obtained index may help interventional cardiologists detect high-risk patients before coronary catheterization, but its application may be restricted to males.