BACKGROUND/AIMS: Gastrointestinal stromal tumor (GIST) constitutes primary nonepithelial neoplasms of the gastrointestinal tract and includes most tumors previously designated as leiomyomas/leiomyosarcomas. GIST is pathologically divided into benign, borderline and malignanct tumor. This study was carried out to delineate the clinical and pathologic features of GIST and to establish the features predicting malignancy. METHODS: Clinicopathologic data of 84 patients who had GIST from 1995 to 1999 were reviewed. RESULTS: The subjects were 42 men and 42 women, and their mean age was 59.3+/-3.2 years. We located fifty-two tumors in the stomach, 28 tumors in the small intestine and 4 tumors in the colorectum years. Histopathology revealed benign tumors in 23 of the 84 patients, borderline tumors in 22, malignant tumors in 39. The average size of tumors was 6.23 cm in diameter (range, 0.6-26 cm). Metastasis was noted in 15.5% of the patients at diagnosis. On endoscopy, ulceration was more common in malignancy. Endosonographic findings except size were not significant statistically. On contrast enhanced computed tomography, malignancy showed more irregular shape and variable attenuation than benign lesions, which seemed to be valuable factor. CONCLUSIONS: The variables predicting malignancy were large tumor size ( 5 cm), location of the colorectum, palpable abdominal mass, ulceration on endoscopy, and less uniformity in shape and variable attenuation on computed tomography.