Gastrointestinal stromal tumors (GIST) are rare mesenchymal tumors of the gastrointestinal tract, the diagnosis of which is difficult. The presence of membrane receptor c-KIT on GIST cells implies their origin from a precursor of interstitial cells of Cajal. Mutations in the c-kit gene result in the constitutive ligand-independent activation of the c-KIT receptor and, consequently, aberrant cell division and tumor growth. Imatinib (STI571), used in the treatment of unresectable GIST, selectively inhibits the enzymatic activity of the tyrosine kinase c-KIT. However, it is known that some mutations in the c-kit gene lead to resistance to imatinib. Therefore, the search for new effective agents is being continued. In this paper the clinical and molecular characterization of the GIST is presented as well as data related to imatinib in the treatment of GIST. Moreover, novel agents for the treatment of patients with advanced GIST are described.