A 46-year-old woman had unsuccessful eradication of Helicobacter pylori. She had history of hypothyroidism with no particular symptoms. Esophagogastroduodenoscopy (EGD) showed chronic atrophic gastritis and numerous 3–5 mm submucosal tumor-like elevated lesions around the gastric body and fundus. Endoscopic ultrasonography (EUS) showed that the submucosal tumor-like lesions were commonly present in the second and third echo layers. Biopsy of those lesions showed the absence of parietal cells, but the presence of atrophic gastritis and neuroendocrine cell hyperplasia with confirmation of immunoreactivity to chromogranin A, consistent with definition of GNETs. Histologically, seven multiple tumors were found. The MIB-1 index was 1% or less, leading to diagnosis of NETs G1. Additionally, blood examinations showed serum gastrin level as high as 5850 pg/ml (standard value: 42–200 pg/ml), and anti-gastric parietal cell antibody was increased 160-fold. Abdominal contrast-enhanced computed tomography (CT) showed no lymph node metastasis or distant metastasis. We diagnosed this patient as having type I GNETs caused by hypergastrinemia due to autoimmune gastritis. Although the patient was also considered for endoscopic surveillance, we decided to perform single-incision laparoscopic antrectomy (SILA) to reduce the need for EGD follow-up. The patient was offered long-term endoscopic follow-up, and she hoped to undergo minimally invasive surgery if surgical treatment could be expected to eliminate the tumors. SILA was performed by a surgeon and a scopist in reverse Trendelenburg position. First, a 3 cm incision was made at the umbilicus under general and epidural anesthesia. A 70 × 70 mm Lap-Protector (Hakko Co., Ltd., Nagano, Japan) was then inserted, and an EZ Access (Hakko Co., Ltd., Nagano, Japan) equipped with two 5 mm trocars and one 12 mm trocar with an evacuation system for surgical smoke was set. Antrectomy without lymph node dissection was performed using a 5 mm 30° forward-oblique viewing endoscope, a vessel sealing device, and linear staplers (Signia Stapling System, Covidien Japan, Tokyo, Japan). To adjust the angle of the device, the EZ access port equipped with three trocars was rotated as appropriate. Reconstruction was by Billroth I reconstruction. Side-to-side anastomosis was performed between posterior sides of the duodenal stump and remnant gastric stump like the delta-shaped anastomosis using 45 mm of purple cartridge Signia Stapling System. The important point is to hang two threads near the small foramen of the remnant stomach and duodenum for delta-like anastomosis and have the assistant pull them out from the 12 mm port. By this procedure, there is no tissue displacement during anastomosis. The surgeon's left forceps act to pull the duodenal stump outward. The stapler entry hole was sutured intracorporeally using the 15 cm 3–0 V-Loc 180 (Covidien, Mansfield, MA, USA), a barbed suture material. The operation time was 140 min and blood loss was 5 ml. There was only one wound in the umbilical region, so the procedure led to good cosmetic results.. The patient had a solid meal on the third day after surgery and was discharged ten days after surgery without complications. Serum gastrin level decreased to 84 pg/ml within the normal range on the day after the operation, and thereafter reverted to the normal range. Although the patient's follow-up period was still short, EGD performed at one year after surgery showed complete disappearance of all lesions of the remnant stomach, a contrast with the large number of GNETs that were scattered throughout the gastric body and fundus that were observed before the operation.