A 63-year-old woman presented to the hospital with persistent nausea, dyspepsia and weight loss for 6 months. Abdomen CT showed a low-attenuation mass, approximately 7.6 cm diameter, in the region of the body and tail of the pancreas. Cystic lesions, 5.5×4.9 cm and 4.6×3.7 cm in size, were observed in the body and tail of the pancreas, respectively, associated with the low-attenuation mass. Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) revealed fetal carcinoembryonic antigen levels of >1000 ng/mL and necrotic cells with no malignant cells. On the basis of the imaging and EUS-FNA results, a putative diagnosis of mucinous cystadenoma accompanying pancreatic adenocarcinoma was made, and distal pancreatectomy and splenectomy were performed. Final biopsy using the surgical specimen confirmed pancreatic adenocarcinoma with moderate differentiation accompanied by degenerative cystic changes.