Aim: We investigated the predictive value of monocyte count to HDL ratio (M/H ratio) for stent thrombosis (ST) in ST elevation myocardial infarction (STEMI). Patients & methods: 1170 STEMI patients treated with primary PCI were followed-up for a median of 37.2 months. Results: During follow-up, 112 patients were diagnosed as 'definite' ST. The rate of ST was significantly highest in the third M/H ratio tertile. In Cox regression analysis, adjusted for other factors, having an M/H ratio in third tertile had a 2.2-fold increased risk of ST. Kaplan-Meier analysis revealed the higher occurrence of ST in the third tertile compared with others (p < 0.001). Conclusion: M/H ratio as a novel marker of inflammation seemed to be an independent predictor of ST in STEMI patients.