Background/Aim. Gastrointestinal (GI) stromal tumors (GIST) are the most common mesenchymal tumors of GI tract. The most frequent localization is gastric (60-70%) followed by intestinal localization (20-30%). The histogenesis, classification, diagnostic criteria and biological behavior of GIST are still discussable. Gastrointestinal stromal tumors are thought to originate from interstitial pacemaker intestinal cells of Cajal. Histologic appearance of a GIST is complicated and biologic potential unpredictable. The aim of of tha study was to investigate anatomic localization , the size of the tumor, incapsulation, microscopic and immunohistochemical characteristics. Methods. The study involved 21 GIST taken by a complete resection in the period from 1994-2006. The analysed parameters were the localization, size, microscopic (mitotic index, nectosis, bleeding, invasivity) and immunohistochemical characteristics (CD117 (ckit), CD34, desmin, vimentin, smooth muscle actin and s- 100 protein expression. Results. Gastrointestinal stromal tumors (n=21) size varied from 10-150 mm were most frequently gastric localised with predominance of malignant tumors (85.72%). Most GIST were comprised of a uniform spindle cell population, but some were dominated by epitheloid cells. Eosinophilic cells stained CD117, CD34 and vimentin positively, were usually arranged in fascicles with the presence of skeinoid fibers. Positive correlation of biologic potential and tumor size, haemorrhagia and mitotic index were found, so as negative correlation of biologic potential and incapsulation. Conclusion. The above results, a specially localization, tumor size, mitotic index, CD117, CD34 and vimentin positivity, may be helpful for setting of a widespread criteria for diagnostic and differential diagnosis of GIST and their use in practice and therapy. .