Background: We report a case of gastrointestinal stromal tumor (GIST) mimicking a left adrenal tumor. Case Presentation: A 62-year-old female was referred to our hospital for the treatment of left adrenal tumor of 2.8 × 2.3 cm incidentally found during her annual checkup. The preoperative diagnosis based on upper gastroscopy and imaging complete examinations was nonfunctional left adrenal tumor possessing malignant potential. Transperitoneal laparoscopic left adrenalectomy was performed. However, the tumor was not found in the excised adrenal gland that had been completely removed during surgery. Repeat computed tomography revealed the presence of the same tumor. Finally, reoperation led us to the true diagnosis of GIST. Conclusion: Many urologists are not familiar with GIST. It is necessary to take GIST into consideration when left adrenal tumor close to the stomach is diagnosed. We discuss the traps which we fell into during the perioperative period in this case.