Peritoneal metastases (PM) of gastric cancer (GC) are characterized by a particularly poor prognosis, with median survival time of 6 months, and virtually no 5-year survival reported. Conversion therapy for GC is defined as a surgical treatment aiming at an R0 resection after systemic chemotherapy for tumours that were originally unresectable (or marginally resectable) for technical and/or oncological reasons. The aim of the present study was to evaluate early and late outcomes in GC patients with PM who underwent the cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC) after neoadjuvant (conversion) chemotherapy. Thirty patients with stage IV GC underwent CRS plus HIPEC. Severe grade III/IV (Clavien-Dindo classification) complications occurred in 13 (43%) patients. The Comprehensive Complication Index (CCI) ranged from 8.7 to 100 (median, 42.4). In the multivariate survival analysis, ypT2 and P3 (according to the Japanese classification of the PM severity) were favourable and adverse prognostic factors p = 0.031 and o = 0.035, respectively. Estimated 1- and 3-year survival was 73.9% and 36.6%, respectively. The median survival was 19.3 months. Conclusion: Conversion surgery, including extended gastrectomy and multi-organ resections followed by HIPEC performed after systemic chemotherapy therapy for GC with PM is justified in downstaged patients with ypT2 and limited (less than P3) PM.