Gastric duplication cysts are rare cystic neoplasms that are often difficult to distinguish from other entities. We describe a healthy 44-year-old woman who presented with acute right lower quadrant abdominal and flank pain as well as chronic nausea and constipation. Her physical examination was unremarkable but contrasted computed tomography revealed a 6 cm cystic lesion between the stomach and body of the pancreas. Endoscopic ultrasonography and fluid analysis were consistent with a mucinous cyst with a markedly elevated fluid carcinoembryonic antigen level. The patient subsequently underwent a laparoscopic distal pancreatectomy, which was converted to an open procedure when the lesion was noted to be adherent to the coeliac axis. Intraoperative endoscopy revealed no abnormality. Final pathology revealed a gastric duplication cyst. The patient recovered well and was asymptomatic on follow-up. In this report, we discuss the incidence, natural history and management of this rare entity.