Over the last decade, gastrointestinal stromal tumor (GIST) became the most commonly diagnosed mesenchymal tumor of the gastrointestinal tract (2,3)Population-based studies suggest an annual incidence of between 11 and 14.5 per million and a prevalence of 129 per million (8). The immunohistochemistry of GIST shows the presence of cellsurface antigen CD117 (KIT), which represents a defining characteristic of GIST (4-7). Immunostaining is essential to differentiate GISTs from other more rare mesenchymal tumors. Differential diagnosis includes leiomyosarcomas, leiomyomas and schwannomas (8). It is believed that GISTs arise from a neoplastic transformation of the intestinal pacemaker cells known as the interstitial cells of Cajal (ICC) (6,9). Prior to 2002, the only available therapeutic option for patients with localized GISTs was surgical resection (10). Unfortunately, even when excised in negative surgical margins, the recurrence rate for lesions larger than 3 cm was found to be significant. Introduction of the first tyrosine k inase inhibitor, imatinib mesylate, has dramatical ly changed the management options avai lable for GIST patients (11). The role of radiation therapy in the treatment of GISTs has not been documented (12). In the past, clinicians were reluctant to use radiation therapy due to concerns over the dose received by normal tissues, mostly the potential gastrointestinal toxicity. As such, radiation therapy has been uti l ized rarely, mostly for pall iation purposes (13). In this report, we describe the successful use of intensity modulated radiation therapy to treat an individual with large intra-abdominal GIST lesions (Figure 1), which were deemed unresectable. An initial attempt at systemic treatment with imatinib was not tolerated by the patient and did not produce a significant response.