The term gastrointestinal stromal tumor was first used in 1983 as a name for gastrointestinal tumors of non- epithelial origin who were negative for immunohistochemical markers for Schwann cells. Gastrointestinal stromal tumors (GIST) are the majority of mesenchymal tumors of the gastrointestinal tract. Their appearance is usually associated with a mutation in the c-KIT gene and in smaller part with a mutation in the platelet derived growth factor receptor alpha (PDGFRA) gene. Tumors are formed from the so-called interstitial Cajal's cells. They occur between 50 and 70 years of age, both in men and women. Much of them are small tumors and are found accidentally while the bigger ones cause various symptoms. The most common symptoms are pressure and pain in the abdomen, bleeding from the GI tract, nausea and in large tumors perforation. Most of the tumors, about 60%, occurs in the stomach, about 30% in the small intestine and only about 5% occurs in the esophagus and colon. Diagnosis is made by endoscopy and radiological methods confirmed by pathohistological examination of the tumor sample and by immunohistochemical analysis using CD117. Treatment is surgery and medication. Small tumors can successfully be operated, but large tumors can only be partially operable and are prone to recurrences. Large tumors can produce distant metastases. Medical treatment is based on inhibitors of c-kit mutation of tyrosine kinase (Imatinib Glivec), and PDGFRA mutations (Sunitinib). Prognosis depends on the size of the tumor, cell atypia, number of mitosis, the depth of invasion and the presence of metastasis.