Upper gastrointestinal submucosal tumor (=subepithelial tumor, SMT) has often been noted during esophagogastroduodenoscopy (EGD). The prevalence of SMT is explosively increasing according to the increase of EGD and EUS. SMT can range from benign lesions to tumors with malignant behavior or potential to become malignant such as gastrointestinal stromal tumors (GISTs). The natural history of SMT is diverse from unconverted to surgical. The aim of this study was to determine the clinical risk factors considering surgery in SMT. Methods: We retrospectively reviewed the medical records of ninety patients who underwent operations due to SMT at Yeungnam University Hospital from January 2006 to December 2010. The size, location, mucosal ulceration, EUS findings and echogenicity of SMT were assessed. Results: The patients` mean age was 55.1 years (standard deviation: 13.12). The ratio of sex was 2:3 (male:female). Of ninety patients, the patients diagnosed as GIST, ectopic pancreas, leiomyoma, Schwannoma, and carcinoid after surgery were 43 (47.8%), 14 (15.6%), 13 (14.4%), 8 (8.9%), and 3 (3.3%) respectively. The average size of operated SMT was 33.3 mm (median: 25.0). (p=0.022) The most common location was the body of stomach (36.6%). The SMT with mucosal ulceration was only 7 cases (7.8%). The preoperative EUS was undergone in 71 patients (78.9%). The most common EUS layer of SMT with checked EUS was muscularis propria (81%). The mitotic index over 50 HPF of GIST was average 4.52 (S.D: 5.18, median: 3.0). The cell type of GIST was reported spindle cell, epithelioid cell, and mixed type, 38 (88.4%), 2 (2.2%), and 1 (1.1%) respectively. The mean size of GIST was 41.7 mm (S.D: 36.55, median: 30). The average follow-up duration was 63.6 weeks. Conclusion: According to our study, we may recommend surgical interventions to middle-aged, female patients with high mitotic index, over 30 mm-sized GIST.