We report a rare case of an epidermoid cyst in an accessory spleen at the pancreatic tail with producing CA19-9. A 55-year-old female was admitted to our hospital, Cancer Research Institute, Kanazawa University, for close examination of a cystic lesion at the pancreatic tail and a high serum CA19-9-value (176 U/mL). There were almost no abdominal symptoms related to the cystic lesion. A cystic tumor approximately 3 cm in diameter and composed of multilocular cysts without a protruding portion of the inner surface was found at the pancreatic tail by ultrasound sonography, computed tomography, and magnetic resonance imaging. Endoscopic retrograde pancreatography revealed that the main pancreatic duct shifted at the pancreatic tail and there was no communication between the main pancreatic duct and cystic lesion. Based on a preoperative diagnosis of mucinous cystic tumor, distal pancreatectomy with splenectomy was performed. Histological findings suggested an epidermoid cyst (3.5 × 3.0 cm) originating from an intrapancreatic accessory spleen. Immunohistochemical analysis of CA19-9 in the epidermoid cyst showed clear staining of the inner epithelium of the cyst and amorphous or hyalinous cystic contents. The serum CA19-9 value was confirmed to decline to normal 2 months after resection. Physicians should not forget this disease during differential diagnosis related to pancreatic cystic lesions with elevated levels of serum tumor markers, such as CA19-9 or carcinoembryonic antigen, although this disease is extremely rare.