Today, obesity is an epidemic problem, especially in developed countries, and it is the second most common preventable disease after smoking that causes death. Surgical treatment is an appropriate and effective option in the treatment of this endemic disease which causes premature deaths with comorbidities. Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor originating from the wall of the gastrointestinal tract. The annual incidence of GIST is reported to be 615 per million. GIST may occur anywhere in the gastrointestinal tract, starting from the esophagus to the anus. It is most frequently settled in the stomach. In our case, we aimed to present a case of mesenchymal tumor incidentally detected during the sleeve gastrectomy.Keywords: Gastrointestinal stromal tumor, obesity; sleeve gastrectomy.