A 43-year-old female patient had high levels of CA19-9 marker; an abdominal ultrasound revealed a cyst. Further investigations with computed tomography (CT), magnetic resonance imaging, and endoscopic ultrasound CT identified a multilocular cystic lesion on the pancreatic tail. An abnormal wall was noted, and different signal strengths were measured in each cyst. Thus, a mucinous cystic tumor was diagnosed, and distal pancreatectomy combined with splenectomy was performed. During the surgery, we identified a multilocular pancreatic cyst with internal bleeding at its distal end. The lesion was ultimately diagnosed as an epidermoid cyst of an intrapancreatic accessory spleen. This diagnosis was based on the histological observation that the vascular construction of the cystic wall was equivalent to that of the spleen, and that its internal tissue was covered by squamous epithelium.