Gastrointestinal stromal tumors (61ST) are an heterogeneous group of non epithelial tumors of the gastrointestinal tract. They are peculiar to extreme cellular variability and uncer tain malignancy. Gist are rare tumors that arise from primitive mesenchy mal cells located in all gastrointestinal tract. Till now they are object of discussion about their origin, diagnostic standards, prognostic factors, histopathological classification. They are more frequently in over 40 years old people without difference in two sex, but they can appear in the child too and in the young man suffering from HIV. The suthors relate two cases of recent observation, and discuss on the biological behaviour of these rare tumors.