Gastrointestinal stromal tumor (GIST) is a rare primary neoplasm of the gastrointestinal tract, mesentery, or omentum. In the past, surgery has been the only effective treatment. The diagnosis and treatment of GIST has been revolutionized over the past decade, since expression of the receptor tyrosine kinase KIT was shown to occur on these tumors. Mutations in this proto-oncogene commonly cause constitutive activation of the KIT tyrosine kinase receptor, an important factor in the pathogenesis of the disease. The development of specific tyrosine kinase inhibitors, such as imatinib mesylate, has led to a breakthrough in the treatment of advanced GIST. Treatment with this drug has led to significant improvements in survival, with overall response rates in excess of 80%. Side effects are common, but usually manageable. The success of this drug has led to further trials investigating its use in the pre- and postoperative situation. This review summarizes the current knowledge of GIST and imatinib treatment and possible future developments.