Background/Aims : Endoscopic ultrasonography (EUS) is a useful technique for demonstrating the muscular origin of gastrointestinal submucosal tumor. This study was to define the EUS features in differential diagnosis for benign and malignant stromal cell tumor. Methods : EUS was performed for 19 patients who had stromal cell tumor confirmed surgically (12 benign cases and 7 malignant cases). Upon the results of EUS, we compared maximum tumor diameter, echo texture, outer margin, presence of cystic spaces, echogenic foci and ulceration between benign and malignant stromal cell tumor. Results: Tumor size, heterogeneity, irregular outer margin and presence of cystic spaces were significantly associated with malignancy. Namely, EUS maximum tumor size greater than 4 cm was observed in 85.7% of the malignancy and 8.3% of the benign stromal cell tumor (p=0.001). Echo-heterogeneity was observed in all of the malignancy and in 8.3% of the benign tumor (p=0.0002). Outer margin was irregular in 85.7% of the malinancy and in none of the benign tumor (p=0.0003). Presence of cystic spaces (>3 mm) was found in 85.7% of the malignancy and in 8.3% of the benign stromal cell tumor (p=0.001). However, presence of echogenic foci (>3 mm) or central ulceration was not associated with the risk of malignancy. Conclusions : The EUS features are significantly important to differentiate malignancy from benign stromal cell tumor and may aid the selection of patients for operative treatment. (Kor J Gastroenterol 1999;34:593 - 600)