Gastrointestinal stromal tumors (GISTs) are rare but are the most common mesenchymal tumor in the gastrointestinal tract. They arise from a precursor cell in the myenteric plexus, and most tumors express a characteristic CD117 antigen, which is part of a tyrosine kinase receptor. This finding has led to the development of novel chemotherapeutic agents targeted at these receptors and has revolutionized the treatment of these tumors, which had been historically disappointing. Surgery is recommended for tumors > 2 cm in size and even has a role in metastatic disease. The approach to tumors < 2 cm in size is more controversial, as these lesions tend to be less aggressive, but the true malignant potential of GISTs can only be determined by surgical resection and histologic evaluation.