Background <p>Gastric sinus abscess is a rare gastrointestinal disorder that is usually difficult to diagnose and is easily misdiagnosed as gastric cancer or tumor in the beginning. Herein, we report a case of gastric sinus abscess for which endoscopy, a common treatment option, was chosen.</p> Clinical data <p>The patient is an elderly woman presenting with abdominal pain as her chief complaint. At first, based on gastroscopy and computed tomography, a bulging lesion of the antrum was seen. Enhanced computed tomography showed a raised hypodense aera in the antrum towards the lumen, surrounded by circumferential enhancement. Endoscopy ultrasound considered gastrointestinal stromal tumor as a possibility. Gastroscopy and ultrasound-guided drainage was performed and sent for pathology, followed by extraction of pus and drainage to flush the lumen. Bacterial culture of the pus yielded specific pathogens, and the patient was discharged on antibiotics with improvement.</p> Conclusion <p>Gastric abscess is a rare but extremely important differential diagnosis of abdominal pain. Early endoscopy is essential for diagnosis and treatment.</p>