Background/aims: Gastrointestinal stromal tumors are considered a specialized group of mesenchymal neoplasms. In this study, the histomorphologic and immunohistochemical features of gastrointestinal stromal tumors are compared with nuclear morphometric results. Methods: Morphometric nuclear parameters such as mean area, mean roundness factor, mean form ellipse, mean length and mean perimeter were evaluated in hematoxylin and eosin. stained slides of 22 gastrointestinal stromal tumors (9 benign and 13 malignant) by using a computer-assisted image analysis system. Morphometric results were compared with tumor behavior and tumor size, the presence of necrosis, mitotic index, and immunohistochemical expressions of p53 and proliferating cell nuclear antigen. Results: We found that tumor necrosis was correlated with mean nuclear roundness factor, mean nuclear form ellipse, mean nuclear length and mean nuclear perimeter (p<0.05). Mitotic index was also correlated with mean nuclear roundness factor and mean nuclear form ellipse (p<0.05). However, no correlation was found between morphometric features and gastrointestinal stromal tumor behavior, tumor size, or index of proliferating cell nuclear antigen and p53 expressions (p>0.05). Conclusions: In this preliminary study, the relative concordance of the morphometric results and general histomorphologic data exhibited the importance of nuclear morphometric analysis in gastrointestinal stromal tumors. Studies including larger series of cases investigating detailed nuclear morphometric analysis of gastrointestinal stromal tumors are needed.