Background: The purpose of the study was to assess the relationship between inflammatory biomarkers (NLR—neutrophil-to-lymphocyte ratio, PLR—platelet-to-lymphocyte ratio, LMR—lymphocyte-to-monocyte ratio, SII—systemic immune-inflammation index) and overall survival in gastric cancer patients. Methods: Over a six-year period (2016–2021), we conducted a longitudinal retrospective cohort research on 549 patients with resectable stomach adenocarcinoma. The overall survival was determined using the univariate and multivariate COX proportional hazards models. Results: The age of the cohort varied between 30 and 89 years old, with an average age of 64.85 ± 10.51 years. Four hundred seventy-six patients (86.7%) had R0 resection margins. Eighty-nine (16.21%) subjects received neoadjuvant chemotherapy. Two hundred sixty-two (47.72%) patients died during the follow-up period. The median survival time in the cohort was 390 days. A significantly lower (p= 0.029—Logrank test) median survival was observed for R1 resections (355 days) in comparison with R0 resections (395 days). Significant differences in survival were observed regarding tumor differentiation, tumoral (T), and node (N) stage. No differences in survival were observed between the low or high value of inflammatory biomarkers (dichotomized by median value in the sample). In the COX univariate and multivariate regression models, elevated NLR proved an independent prognostic factor for lower overall survival [HR = 1.068, (95% CI 1.011–1.12)]. In this study, the other inflammatory ratios (PLR, LMR, and SII) did not prove as prognostic factors for gastric adenocarcinoma. Conclusions: In resectable gastric adenocarcinoma, elevated NLR before surgery was associated with lower overall survival. PLR, LMR, and SII had no prognostic value for the patient’s survival.