Two hundred and seventy-seven patients with advanced carcinoma of the stomach invading the serosa were studied with regard to the relationship between the length of the serosal invasion (LSI) and prognosis, with a division made between expanding and infiltrative types of tumors. Among patients with expanding types of tumors, five year survival rates were 40 per cent in patients with LSI less than 4.0 centimeters, 33 per cent in patients with LSI 4.1 to 6.0 centimeters and 13.0 per cent in patients with LSI more than 6.0 centimeters. Among those patients with infiltrative types of tumors, those with less than 2.0 centimeters of LSI had a better prognosis (five year survival rate of 53 per cent), whereas those patients with a LSI more than 2.0 centimeters had a very poor prognosis (five year survival rate of less than 20 per cent) and the significant LSI on prognosis was found to be 2.0 centimeters. Involvement of the lymph node and metastasis to the liver were not affected by LSI, whereas the rates of peritoneal dissemination and direct invasion to neighboring organs increased with an increase in LSI. Knowledge of these factors facilitates the planning of postoperative treatment.