BACKGROUND/AIMS: Mesenchymal tumors are the most frequent submucosal tumors in gastrointestinal trail. We reviewed the mesenchymal tumors which are confirmed by pathology to examine whether the invasive approach of all mesenchymal tumors is necessary. METHODS: This study was performed on fifty-nine patients who has mesenchymal tumors confirmed by endoscopic or surgical resection from January 2000 to June 2004. RESULTS: Mesenchymal tumors consisted of thirty-six gastrointestinal stromal tumors (GISTs), 20 leiomyomas and 3 schwannomas. All the esophageal tumors were leiomyoma (12/12, 100%). In stomach, there were 32 GISTs (76.2%), 7 leiomyomas (16.7%) and 3 schwannomas (7.1%). And there were 4 GISTs (80.0%) and 1 leiomyoma (20.0%) in duodenum. Tumors less than 1 cm in maximal diameter were leiomyoma or GISTs with very low risk of aggressive behavior. 56.1% of the tumors larger than 1 cm consisted of low, intermediate or high risk GISTs. CONCLUSIONS: Biopsy must be considered according to its size and anatomic location of mesenchymal tumors. The invasive approach for every esophageal submucosal tumor is not necessary unless the size is very large, because most of them are benign in nature. However, the gastric submucosal tumor with more than 1 cm in diameter should be carefully and regularly followed up or biopsied because it cannot be assumed to be benign for any GIST more than 1 cm in size at the present time, safely.