With the application of our endoscopical method of contrasted X-ray imaging, gastric submucosal tumors were studied with chief regards to their modes of growing up and patterns of development. It has become known that, of extra-gastric developing tumors, larger ones tend to show Pattern IVa and smaller ones Pattern IVb. Generally, the tumors showed a tendency of becoming larger in older patients. Periodical checking disclosed about 15% of the tumors growing larger with the lapse of time. It has been surmised that as tumors grow up, their development possibly turns from intra-gastric to intramural and mingled in pattern. Their modes of growing could be classified as follows: Abruptly growing large at a certain time and then remaining without notable changes, step-by-step enlarging, and gradually growing up straight forwardly with years.