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287 Background: As recent advances in chemotherapy improved prognosis of gastric cancer (GC) patients with peritoneal metastasis (PM), accurate diagnosis of PM has become more important. However, the sensitivity of conventional imaging modalities such as CT or PET is not satisfactory. Staging laparoscopy (SL) is often used to diagnose PM in advanced GC patients, but accurate detection of PM can be difficult. In this study, we evaluate the usefulness of laparoscopic narrow-band imaging (NBI) versus conventional laparoscopic white-light imaging (WLI) for the diagnosis of PM and for the evaluation of therapeutic effect of chemotherapy. Methods: We excised 54 white nodules from the parietal peritoneum of 40 GC patients. Among them, 9 patients received chemotherapy for advanced or recurrent GC before SL, and 31 did not receive chemotherapy except for adjuvant chemotherapy with S-1. The WLI and NBI findings were compared with the pathological findings. Results: Intranodular vessels were evaluated by WLI and NBI for dilatation, tortuousness, heterogeneity, and brown spots. Detection of any one abnormal finding on NBI plus clear demarcation of the peritoneal nodules on WLI more properly diagnosed 42 peritoneal nodules of 31 patients who did not receive chemotherapy (sensitivity, 100%; specificity, 88.9%; accuracy, 95.2%). In contrast, diagnosis ability was poor for 12 peritoneal nodules of 9 patients who received chemotherapy before SL (sensitivity, 66.7%; specificity, 33.3%; accuracy, 58.3%). Conclusions: Laparoscopic NBI is a useful tool for the diagnosis of PM in advanced GC before chemotherapy, and disappearance of dilated vessels on laparoscopic NBI could be useful to evaluate the therapeutic effect.