In advanced gastric cancer, the frequency of relapses such as metastasis to the peritoneum is high. For this reason, prognostic and treatment methods were studied. In 457 cases in which diagnostic cytology was utilized, 36 (61%) of the 59 cases in which dissemination had been macroscopically observed (P 1) were positive. Moreover, 13 cases of P 0 were also positive. The prognosis of the positive cases was worse, but there was not a significant statistical difference between the positive and negative cases. Chemotherapy has become the most common treatment because of the appearance of new anticancer drugs. TS-1 and paclitaxel were repeatedly administered in 10 cases, and the median survival time was 17 months. These drugs were effective even in carcinoma of the peritoneum, and an improvement in the prognosis can be expected. Surgery was performed in 23 cases due to stenosis of the digestive tract, and in 21 cases the patients were able to eat after surgery. The median postoperative survival time was 7 months, and surgery improved the prognosis. The improved sensitivity of diagnostic cytology and the standardization of chemotherapy and surgery warrant further study.