Aim: We present an unusual case of malignant gastrointestinal stromal tumor filling the entire abdominal cavity. Introduction: Gastrointestinal stromal tumors are the most common mesenchymal neoplasms of the gastrointestinal tract. Small tumors are generally benign, but large tumors disseminate to the liver, omentum and peritoneal cavity. They rarely occur in other abdominal organs. Material and Metods: The operative material consisted of segment of ileum where a tumor mass of 8 cm was found originating from the wall and fragments of small intestinal serosa and omentum where multiple nodular tumor mases were found. Representative samples were taken, and were paraffin embedded and stained routinely with Hematoxyllin-Eosin. Additionally immunohistochemical analyses were performed using the antibodies c-kit, CD34, Vimentin, CKAE1/AE3, Ki67 and others. Results: Microscopic analysis revealed a malignant gastrointestinal stromal tumor with a high mitotic rate of 58/50 HPF mitoses. However clinical reports stated that an additional large 12 cm tumor mass was found in the liver that was not removed. Conclusion: Gastrointestinal stromal tumors are the most common gastrointestinal mesenchymal neoplasms but presence of multiple tumor masses on various organs and sites is rare. Presence of multiple tumors in various organs brings about the issues of possibility of multiple primaries or the proper detection of the original tumor mass.