Objective: Inflammation is one of several etiopathological mechanisms contributing to bipolar disorder. Neutrophil-lymphocyte ratio (NLR), monocyte-lymphocyte ratio (MLR), and platelet-lymphocyte ratio (PLR) are relatively cheap hematological parameters recommended to measure the level of inflammation. In this study, the NLR, MLR, and PLR values of the same patients during manic and euthymic periods were compared to a healthy control group. Methods: This retrospective study was conducted on inpatients with bipolar disorder manic episodes at the University Faculty of Medicine psychiatry clinic. Ninety-nine patients with manic episodes of bipolar disorder and age and gender-matched 101 volunteers without prior psychiatric illness were included in the study. Neutrophil, lymphocyte, monocyte, and platelet counts during the disease period were recorded, and NLR, MLR, and PLR values were calculated from these values. Similar hematological parameters of the same patients in the euthymic period after discharge were compared. Results: Patients with manic episodes were shown to have significantly higher neutrophil, platelet, NLR, MLR, and PLR levels than the control group (p<0.001). Monocyte count was significantly lower in manic episode patients compared to controls (p<0.001). Neutrophil and monocyte counts were significantly lower during the euthymic period compared to the control group, while NLR, MLR, and PLR levels were higher (p<0.001). Conclusions: The fact that NLR, MLR, and PLR are higher in BD patients compared to the healthy control group in both manic and euthymic periods indicates that they can be used as trait biomarkers.