Background: Gastric cancer (GC) with peritoneal metastasis (PM) has a dismal prognosis. Palliative systemic chemotherapy (SC), usually doublet combinations of platinum and fluoropyrimidines, is the standard of care. Pressurized IntraPeritoneal Aerosol Chemotherapy with Cisplatin and Doxorubicin (PIPAC C/D) yields promising results. Here we aimed to compare overall survival (OS) between SC + PIPAC C/D vs. SC alone in patients with PM from GC. Methods: Prospective cohort of 95 consecutive patients with PM from GC treated in palliative intent at our institution from 2010 to 2018. Of these patients, 69 received SC + PIPAC C/D („PIPAC“), 26 SC alone („control“). Choice of treatment was not dictated by medical criteria, but by (non-) availability of the single-use medical devices needed for PIPAC in Russia. All patients received doublet or triplet chemotherapy with platinum together with fluoropyrimidines or capecitabin. A Cox proportional hazard model based on propensity score (PS) was used to assess the effect of PIPAC on OS and account for confounding factors. Results: The HR adjusted for PS for PIPAC vs. control was 0.396 (CI 5- 95% = 0.224-0.700, p-value 0.001). In the simple (unadjusted) Kaplan-Meier, median survival in the control group was 7.0 months (CI: 4.51 - 9.49) and in the PIPAC group 14.0 months (CI: 11.46-16.54). In the control group, all 26 patients died after 1-25 months. In the PIPAC group, 36 of 69 patients died after 4 to 20 months. The longest observed survival time in the PIPAC group was 27 months. Significance for the log-rank test after Mantel-Cox (not adjusted) was p < 0.0001. Conclusions: Compared with SC alone, intensified chemotherapy combining PIPAC C/D and SC doubled OS. These promising results need to be confirmed in a randomized trial.