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Schwannoma is a peripheral nerve tumor that arises from the neural sheath, generally solitary and benign. Retroperitoneal location is rare, less than 6%, and often asymptomatic until the tumor reaches a large size and causes compressive symptoms. Schwannoma is difficult to diagnose by conventional imaging features alone, and so diagnosis is commonly confirmed with surgical resection. Endoscopic ultrasound (EUS) fine-needle aspiration (FNA) is useful for the preoperative diagnosis and the following treatment plan, although the diagnostic accuracy rate is rather low. EUS fine needle biopsy (FNB), with improved needle designs, has shown increasingly better diagnostic accuracy even in extrapancreatic solid lesions. We report a case of a retroperitoneal schwannoma successfully diagnosed before surgery by EUS-guided FNB.