This is the first case of gastric schwannoma that exhibited increased accumulation of [(18)F] fluorodeoxyglucose (FDG) on positron emission tomography (PET) imaging. The patient was a 60-year-old woman in whom esophagogastroduodenoscopy showed a submucosal tumor, about 25 mm in size, in the upper body of the stomach, with ulceration at the top of the tumor. Endoscopic ultrasonography revealed a well-defined hypoechoic mass located in the proper muscle layer of the stomach. The specimen taken from the tumor showed only inflammatory degenerative tissue. Abdominal computed tomography revealed a tumor in the upper body of the stomach. FDG-PET showed FDG uptake (standardized uptake value [SUV] max 5.8) coincident with the tumor. Hence, the tumor was diagnosed initially as a gastrointestinal stromal tumor of the stomach. Laparoscopic partial gastrectomy was performed. Pathological examination showed that the tumor consisted of spindle cells with large nuclei, and mitosis was absent. The Ki-67 labeling index of the tumor cells was 4%. Immunohistochemically, the tumor cells showed a positive reaction for S-100 protein, whereas they were negative for KIT, CD 34, and alpha-smooth muscle actin protein. The tumor was diagnosed as a benign gastric schwannoma. Gastric schwannoma should be included in the differential diagnosis of submucosal tumors of the stomach with FDG uptake.