INTRODUCTION: Gastric duplication cysts (GDCs) are rare congenital anomalies, usually diagnosed in childhood, but can occasionally present in adults with non-specific symptoms such as abdominal pain, nausea, vomiting, and dysphagia. Advanced imaging, particularly endoscopic ultrasonography (EUS), plays a crucial role in diagnosis, while surgical or endoscopic resection is the definitive treatment. PRESENTATION OF CASE: An 18-year-old female with no significant medical history presented with recurrent epigastric pain radiating to the back, abdominal fullness, heartburn, and difficulty swallowing solid foods for one month. Upper endoscopy revealed a gastric mass, and EUS identified a 30 - 28 mm cystic lesion adjacent to the stomach fundus. Fine-needle aspiration confirmed the diagnosis of a gastric duplication cyst. The patient underwent successful endoscopic unroofing, leading to symptom resolution. CLINICAL DISCUSSION: GDCs in adults are uncommon and often present with vague gastrointestinal symptoms, making diagnosis challenging. Imaging modalities such as EUS and fine-needle aspiration are essential for differentiation from other gastric lesions, including gastrointestinal stromal tumors and pancreatic cysts. Traditional management involved surgical resection, but endoscopic approaches, such as unroofing, offer a less invasive alternative with favorable outcomes. CONCLUSION: This case emphasizes the need for GDCs to be considered in the differential diagnosis of gastric masses. Early identification with EUS and minimally invasive intervention, such as endoscopic unroofing, can effectively resolve symptoms and prevent complications.