Background <p>Positive peritoneal cytology (CY1) is classified as stage IV gastric cancer and typically treated with systemic chemotherapy. However, upfront surgery is sometimes performed when CY1 is identified intraoperatively or postoperatively and may improve long-term survival when followed by adjuvant chemotherapy. It remains unclear which patients benefit most from this approach. This study aimed to identify patient subgroups likely to achieve long-term survival with upfront surgery followed by adjuvant chemotherapy.</p> Methods <p>We retrospectively analyzed patients diagnosed with P0CY1 who underwent upfront surgery between 2008 and 2020. Prognostic factors for overall survival (OS) and progression-free survival were evaluated using univariate and multivariate analyses.</p> Results <p>A total of 147 patients were included; 65% were male, with a median age of 72 years. Macroscopic types 3 and 4 were present in 80% of patients, 91% had pathological T4 tumors, and 63% had lymph node metastasis. Total gastrectomy was performed in 54%, and 81% received adjuvant chemotherapy. Median OS was 27.0&#xa0;months. Univariate analysis showed age, macroscopic type, tumor size, and adjuvant chemotherapy were significantly associated with OS. Multivariate analysis identified adjuvant chemotherapy tumor size  ≥  80 mm, and macroscopic types 1 and 2 as independent favorable prognostic factors. Among patients receiving adjuvant chemotherapy, those with macroscopic types 1 and 2 had significantly better OS (5-year OS rate: 46%) compared to types 3 and 4.</p> Conclusions <p>In P0CY1 gastric cancer, upfront surgery followed by adjuvant chemotherapy may result in long-term survival, particularly in patients with macroscopic types 1 and 2.</p>