Background: Preeclampsia is a serious complication of pregnancy with negative consequences for the mother and fetus. It was aimed to investigate whether the systemic immune inflammation index is a parameter that will facilitate the diagnosis of preeclampsia. Methods: This retrospective and single-center study included patients diagnosed with preeclampsia after admission to the emergency department and those who met the inclusion criteria. Vital parameters, demographic data, medical history, white blood cell count, platelet count, neutrophil count, systemic immune-inflammation index values, biochemical parameters, and gestational weeks were analyzed in each patient. Results: A total of 40 patients with preeclampsia (preeclampsia group) and 40 normal pregnant women (control group) were included. Laboratory tests revealed that the mean WBC, neutrophil, and lymphocyte counts were significantly higher in the preeclampsia group than in the control group, whereas the preeclampsia group had a significantly lower mean platelet count than the control group (p