More accurate preoperative staging is necessary to determine the treatment strategy for locally advanced gastric cancer. Thirty-two patients with T3 or T4 gastric cancer expected to undergo curative resection based on conventional examinations underwent staging laparoscopy. The disease stages determined were compared with those obtained by conventional methods. The discrepancy rate of disease staging was 16 of 32 (50.0%), with down-staging in 5 of 32 (15.6%) and up-staging in 11 of 32 (34.4%). Of the 32 patients, 13 (40.6%) were found to have unsuspected peritoneal dissemination. The positive predictive value for peritoneal metastasis by staging laparoscopy was 100%, whereas the negative predictive value was 89% (17/19). The accuracy rate was 94%. After laparoscopy, 15 of the 32 (46.9%) were diagnosed as candidates for curative resection. Of these 15 patients who underwent surgery, 13 (86.7%) underwent curative resection (1 R0 and 12 R1); the remaining two underwent R2 resection because of peritoneal metastasis that was undetected by staging laparoscopy. Patients with tumors judged noncurable by laparoscopy (n = 11) received neoadjuvant chemotherapy. In 7 of the 11 cases, salvage surgery was done (one R0, three R1, three R2 resections). A second staging laparoscopy was performed in four cases to determine the indication for salvage surgery. Three of the four were judged to be curable and underwent curative resection. Staging laparoscopy is an effective tool for detecting unsuspected peritoneal metastasis, and it can increase the curative resection rate and decrease unnecessary laparotomy for advanced gastric cancer. Second-look laparoscopy enables accurate assessment of the chemotherapeutic response, which can help in decisions about salvage surgery.