A 50-year-old man presented to the emergency department with a 1-day history of severe epigastric pain, vomiting and fever. He had a background of alcohol excess and smoking. The patient was tachycardic and febrile with an elevated white blood cell count and C reactive protein. CT demonstrated extensive upper abdominal free fluid, without free air, with a large cystic lesion arising from the greater curvature of the stomach, and a second smaller cystic lesion arising from the posterior aspect of the gastric fundus. The patient was managed with nasogastric drainage, parenteral nutrition, intravenous antibiotics and proton pump inhibitors, and CT-guided abdominal drainage, with resolution of sepsis, and further outpatient care was transferred to our unit. Follow-up endoscopy demonstrated a diverticulum arising from the posterior aspect of the gastric fundus, with normal mucosa throughout the remaining stomach, while CT showed an additional cystic lesion arising from the greater curvature, with thickening of the adjacent gastric wall consistent with a gastric duplication cyst (GDC). Laparoscopy confirmed a small diverticulum at the fundus, and a large GDC anteriorly with associated omental adhesions consistent with prior perforation—two wedge resections were performed. Histology demonstrated no evidence of malignancy or ectopic mucosa. The patient recovered uneventfully and remained free from recurrent symptoms at 6 weeks postoperatively. GDC is a rare entity, which may be associated with ectopic mucosa, malignant transformation and upper gastrointestinal perforation. No previous report describes the coexistence of a GDC and gastric diverticulum. Herein we describe the investigation and management of this condition, and review the associated peer-reviewed literature.