Background: Increasing amounts of evidence suggest patient-related systemic inflammatory response (SIR) as a powerful prognostic factor in cancer and applicability of SIR as a prognostic factor has been investigated. Aim: To evaluate the prognostic significance of SIR, which is among routinely analysed blood parameters in patients with all stages of gastric cancer (GC). Methods: A total of 245 patients with gastric cancer who were followed up and treated in four clinics of medical oncology were included in the study. At first admission of the patients, from routinely determined whole blood cell counts in medical oncology clinics, their neutrophil/lymphocyte ratio (NLR) and platelet/lymphocyte ratio (PLR) values were estimated and recorded before initiating chemo-or radiotherapy. A univariate non-parametric analytical method and chi-square test examined the correlation between prognostic factors, and survival rates. Survival curves were estimated using the Kaplan-Meier method. Results: Sixty-eight (27.8%) female and 177 (72.2) male patients (total n=245) were included in the study. When NLR was used as an indicator of SIR, 108 (44.1%) patients were SIR negative and 137 (55.9%) patients were SIR positive. When PLR was used as an indicator of SIR, SIR negativity and positivity were detected in 93(38%) and 152 (62%) patients, respectively. A statistically significant correlation was found between status of lymph node metastasis, stage of the disease and NLR (P=0.001, P=0.017). SIR determined with PLR was found to be correlated with the depth of tumor invasion and stage of the disease (P=0.016, P=0.033). A significant correlation was not detected between PLR and survival (P=0.405). Conclusion: According to our study, parameters of NLR and PLR calculated preoperatively from peripheral blood samples can be used in patients with various sizes of tumours in different disease stages. Still based on our results, NLR calculated during diagnostic workup is a parameter with a prognostic value. In addition, NLR is a determinative factor in the selection of surgical method and chemotherapeutic modalities, which also functions as a potential contributory marker in effective immunotherapeutic strategies.