Background: The prognosis in gastric cancer is highly dependent on 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 intraperitoneal chemotherapy (HIPEC) may affect the long-term outcomes in this group of patients, but high morbidity associated with such treatment provides the rational to identify the correct population of patients for HIPEC. Methods: This is the long-term effect analysis of prospectively observed cohort of patients assessed with immunocytochemistry peritoneal lavage in the single reffereal center. Between January 2002 and November 2004, the total of 140 patients with histologically confirmed gastric cancer were enrolled to the study. Laparotomy and intraoperative peritoneal lavage for immunocytochemistry examination were performed prior to gastrectomy. The fluid recovered was centrifuged and the sediment was fixed in 10% buffered formalin for 24 h, embedded in paraffin and cut into 4 µm-thick sections. Microscopic slides were also stained against cytokeratin 19 (CK-19), cytokeratin AE1/AE3 (CK-AE1/AE3) and mesothelioma marker. All patients were followed up with endpoints of cancer recurrence and mortality. Results: Median overall survival (OS) in patients with immunocytochemical evidence of free cancer cells in peritoneal washes was significantly shorter than in those without (11 [range: 2-55] vs. 45 [range: 1-164] months). The two groups differed significantly in long-term survival (5-year OS rate: 0.0% [0/17] vs. 43.1% [53/123]; 10-year OS rate: 0.0% [0/17] vs. 29.3% [36/123]) (p < 0.001). Positive peritoneal washing immunocytochemistry was an independent poor outcome prognostic factor after correction for all major prognostic factors. Conclusions: Positive peritoneal washing immunocytochemistry correlated with clinical staging of gastric cancer and was associated with poor overall survival (OS). With all patients dying in 5 years, this subgroup of patients defines a clear population for early salvage HIPEC for prospective verification.