Prognosis in gastric cancer patients is highly dependent on the tumor stage at presentation. Surgery still remains the main therapeutic option in gastric cancer patients. However, the efficacy of this treatment may be substantially limited by the risk of peritoneal dissemination. The introduction of hyperthermic intraperitoneal chemotherapy (HIPEC) may affect the long-term outcomes in this group of patients, but high morbidity associated with this procedure provides the rationale to identify the correct population of patients for HIPEC. The aim of the study was to evaluate a long-term prognostic value of peritoneal washing immunocytochemistry as a prognostic factor in patients with gastric cancer. This is a prospective, long-term analysis of patients who underwent peritoneal lavage with immunocytochemistry assessment in the Maria Sklodowska-Curie National Research Institute of Oncology, in Warsaw, Poland. Between January 2002 and November 2004, a total of 157 patients with histologically confirmed gastric cancer were enrolled in the study. Laparotomy and intra-operative peritoneal lavage for immunocytochemistry examination were performed prior to gastrectomy. All patients were followed up with endpoints of cancer recurrence and mortality. Positive peritoneal washing immunocytochemistry was associated with clinical staging of gastric cancer, overall survival, and progression-free survival. It is an independent poor outcome prognostic factor.