Gastric adenomyoma is a rare benign tumor, characterized by gland-like structures embedded within a smooth muscle stroma. We report the case of a 26-year-old woman with a body mass index (BMI) of 51 kg/m2 who was not having any metabolic diseases was prepared for obesity surgery. No pathologies were detected in the abdominal ultrasound or upper gastrointestinal system endoscopy taken before the operation. Abdominal computerized tomography was obtained which revealed a nodular lesion causing mural thickening on the anterior wall of the antrum. The mini-gastric bypass surgery procedure was performed with subtotal gastrectomy to remove the mass. The final diagnosis of gastric adenomyoma was made. Although gastric adenomyomas are rare, they should always be kept in mind in the differential diagnosis of extramucosal gastric lesions.