A 28-year-old female presented with a huge intra-abdominal mass. Initially a mesenteric mass was diagnosed, but her tumor was found to be a gastrointestinal stromal tumor (GIST). Laparotomy was performed. The mass was resected en bloc with clear surgical margins in January 2007. It was found to be 20 × 18 × 16 cm. In order to remove the tumor, the left half of transverse colon with its mesocolon, spleen, body and tail of pancreas, and a part of the small intestine had to be removed. The mass was tightly attached to these viscera. The tumor was surgically removed three years ago. The pathology report of the case presented places the tumor in the high-risk category. The tumor had a relatively high mitotic index. It was positive for CD117 and CD34 stains and also positive for smooth muscle actin. Although the patient did not receive adjuvant chemotherapy, no signs of local recurrence or distant metastasis could be recognized on follow up. Surgery remains the standard initial management for all localized GISTs. The tumor should be removed en bloc, with clear surgical margin. The case presented indicates no association of tumor size with early local recurrence of the tumor or early distant metastasis.