Aim: Thyrotoxicosis is a clinical state of inappropriately high levels of free T4 (thyroxine) and/or free T3 (tri-iodothyronine)in the body caused by distinct etiologies including Graves’ disease (GD), subacute thyroiditis (SAT), toxic adenoma and toxicmultinodular goiter (TMNG). Simple hematologic indices such as neutrophil/lymphocyte ratio (NLR), platelet/lymphocyteratio (PLR) and mean platelet volume (MPV) have increasingly been mentioned as measures of presence and severity ofthyrotoxicosis. In this study, we aimed to analyze whether there is a link between these peripheral blood parameters and thepresence of thyrotoxicosis.Material and Method: A total of 46 GD, 46 TMNG, 39 TA and 45 SAT patients and 45 healthy controls were included.Laboratory parameters and NLR, PLR, and MPV values were recorded from peripheral blood complete blood cell counts foreach patient.Results: This study showed that NLR and PLR levels are elevated in patients with SAT in comparison with other thyrotoxicpatient groups and controls. The post hoc analysis of comparison of NLR and PLR in each study groups revealed that NLRand PLR were statistically different in the SAT group in comparison to the GD, TMNG, TA, and healthy controls. A significantdecrease in the level of MPV was demonstrated in thyrotoxicosis patients (p<0.001).Conclusion: NLR, PLR and MPV that is routinely and automatically calculated from complete blood count plays an importantdiagnostic role in thyrotoxicosis.