Aim: Recently, lymphocyte-to-monocyte ratio (LMR) has emerged as a new indirect marker of inflammation which is associated with adverse outcomes in oncology and cardiovascular diseases. The aim of the study was to evaluate the relationship between LMR and slow coronary flow (SCF). Patients & methods: A total of 100 consecutive patients with SCF and 100 consecutive patients with normal coronary flow were enrolled in this study. Results: LMR was significantly lower in patients with SCF than in patients with normal coronary flow (p < 0.001). Also, LMR was negatively correlated with neutrophil-to-lymphocyte ratio and CRP levels (p < 0.001 and p = 0.005). LMR was found to be significantly and independently associated with SCF (p = 0.033). Conclusion: LMR was negatively correlated with serum C-reactive protein and neutrophil-to-lymphocyte ratio levels.