Gastrointestinal stromal tumors (GISTs) are the most frequent mesenchymal tumors of the gastrointestinal tract. Major advances in their definition and classification and the understanding of their molecular mechanisms have recently been made. These advances have become a model of targeted therapy in oncology. The diagnosis of GISTs relies on histological arguments - proliferation of spindle cells, seldom of epithelioid cells or both spindle and epithelioid cells - and on immunohistochemical arguments - expression of CD117 usually associated with CD34 expression. The evaluation of the prognosis is essential and based on a simple algorithm using two prognostic parameters, tumor size and mitotic index. The aim of this paper is a complex histopathological assessment, using both classic and modern (immunohistochemistry) techniques, of the GISTs comprised in the study. GISTs occur mainly in older adults (median age 60-69 years), anywhere along the gastrointestinal tract but also retroperitoneal. Most of them were nodular (75%), tumor necrosis and mucosal ulceration being the most frequent encountered secondary alterations; these modifications proved to be significantly correlated with large tumor size and high malignancy. Immunohistochemical evaluation revealed that 77 (97%) cases of GISTs presented a positive reaction for CD117, 50 (63%) cases were positive for CD34, 19 (24%) were positive for SMA and only 10 (13%) were positive for S100. Immunohistochemical evaluation remains an important tool of pathology in the diagnosis of GISTs, in the differential diagnosis from other gastrointestinal mesenchymal tumors and represents the gold standard for diagnosis of these tumors and an eligibility criterion for imatinib therapy.