To assess changes in monocyte-to-high-density lipoprotein (HDL) ratio (MHR), neutrophil-to-lymphocyte ratio (NLR), and systemic immune-inflammation index (SII) with Graves' ophthalmopathy (GO) and their possible relation with GO disease activity and severity. A total of 20 patients with GO and 24 healthy controls were involved in the study. The thyroid status, MHR (monocyte count/HDL cholesterol level), NLR (neutrophil count/lymphocyte count) and SII [(neutrophil count × platelet count)/lymphocyte count] were compared between the groups. The relation of systemic inflammation parameters with disease activity and severity was evaluated. The mean Clinical Activity Score (CAS) was 0.75 ± 0.78 in the GO group. None of the patients were active. The severity was mild for 14 (70.0%) patients and moderate-to-severe for 6 (30.0%) patients. MHR (17.28 ± 5.56 vs. 13.28 ± 5.08), NLR (2.51 ± 1.09 vs. 1.69 ± 0.53) and SII [600.42 (391.79-837.16) vs. 413.69 (344.26-603.82)] values were significantly increased in GO patients than in the controls (p = 0.017, p = 0.005 and p = 0.036, respectively). CAS was significantly correlated with MHR (r = 0.815, p < 0.001), NLR (r = 0.768, p = 0.017) and SII (r = 0.837, p < 0.001). The severity of GO was associated with increased MHR, NLR and SII (p = 0.019, p = 0.036 and p = 0.008, respectively). ROC analysis demonstrated that MHR, NLR and SII have a good ability to differentiate GO patients from healthy individuals. GO patients have higher MHR and SII levels than healthy controls. Higher MHR, NLR and SII values were associated with increasing disease severity and activity, supporting the efficacy of these non-invasive, low-cost markers in determining the course of GO. Future prospective controlled trials are needed to elucidate the relation between inflammatory markers and GO.