Intestinal duplication is a rare congenital disease. It appears throughout the gastrointestinal tract, especially in the ileum. Here we describe the rare case of a gastric duplication cyst in a 59-year-old patient. Diagnostic findings and surgical therapy are discussed. Gastric duplications in adults are extremely rare, and diagnosis is often missed. Symptoms are unspecified pain in the upper abdomen, vomiting and fever, with some patients having weight loss. Complications are rare. Chronic infections and ruptures are described. For diagnosis, CT scan with oral contrast is preferred. Endoscopy is negative in most cases. Therapy is surgery. Local excision of a small wall of gastric mucosa is sufficient in most cases, but sometimes a subtotal gastrectomy is necessary.