Surgery for gastric cancer in Japan has frequently been combined with resection of the spleen (splenectomy) or of the pancreatic body and tail and spleen (pancreatosplenectomy, PS). Splenectomy in patients with gastric cancer has been performed with two major purposes in mind: (1) curability of the cancer and (2) immunologic reasons. Direct cancerous invasion to the pancreas requires PS, although examination of these cases revealed that in 34.3% of such macroscopic invasions only fibrous adhesion to pancreas existed. Metastases to lymph nodes at the splenic hilus (no. 10) or along the splenic artery (no. 11) also required splenectomy. The incidences of no. 10 or no. 11 lymph node metastasis were as high as 26.7% and 22.2% respectively, for cancers of whole stomach, and 15.5% and 12.1% for cancers of the upper portion of stomach. Concerning the immunologic aspect of splenectomy for gastric cancer, the reports of fundamental research and clinical studies suggest that the spleen plays sometimes acts as a suppressor and at other times as a helper to the tumor activity, according to the number of tumor cells. From these data, we concluded that the spleen should be preserved in stage I, II, and III patients with curative operation; for stage IV patients the spleen should be resected. The immunologic significance of splenectomy should be clarified precisely in the near future.