CT is a valuable method for preoperative staging of patients with stomach cancers. However, in patients with poor distension of the stomach and scanty fat between the stomach and adjacent organs, CT findings may indicate a false impression of gastric wall thickening and cannot provide the precise extent of stomach cancer. We studied the usefulness of gastric distension by gas-forming agent in 28 cases of pathologically confirmed gastric cancerson CT. Comparitive analysis between CT findings and surgical pathologic findings was done in 22 cases who underwent surgery. The results were as follows: 1. Conventional CT failed to define the wall thickening or masses ofthe stomach, in 14 cases of 23 advanced gastric cancers, while CT with gas distension technique allowed good visualization in all advanced gastric cancers. 2. In 2 cases of 5 early gastric cancers, CT with gas distensiontechnique could detect focal thickening of the gastric wall, even less than 1cm thickness. 3. Among 13 cases within distinguishable border between stomach and liver on conventional CT, 7 cases were diagnosed as negative invasionon CT with gas distension technique and 5 cases of these were confirmed by surgery. 4.Among 11 cases within distinguishable border between stomach and pancrease on conventional CT, 3 cases were diagnosed as negativeinvasion on CT with gas distension technique, all of which were confirmed by surgery. 5. There was no significant difference between conventional CT and CT with gas distension technique of the stomach to diagnose invasion intotransverse colon, transverse mesocolon, lymph node metastasis, and various distant metastasis. Our experience suggests that CT with gas distension technique should be a reliable method in determining tumor localization and direct invasion into adjacent structures, such as liver and pancreas.