Gastrointestinal duplication is a rare congenital disease which affected more commonly the ileum, while the stomach is rarely involved. Generally diagnosed in paediatric or young age, it could be difficult to suspect a gastrointestinal duplication in adults. Herein, we report a 55-year-old male with a gastric duplication cyst found on routinely checkup for chronic hepatitis and first misdiagnosed as a gastrointestinal stromal tumor (GIST); we also discuss its embryology.