Few reports of mucinous cystic neoplasm (MCN) in association with anaplastic carcinoma exist. The present study reported an unusual case of a 25-year-old female exhibiting large pancreatic MCN with anaplastic carcinoma. Notably, the patient was a Jehovah's Witness and therefore refused any blood transfusions. Preoperative diagnosis was invasive pancreatic MCN measuring 12.5 cm with ascites. Distal pancreatectomy was performed in combination with splenectomy and partial resection of the transverse colon. Intraoperative estimated blood loss was 400 ml, therefore a blood transfusion was not required. The patient had an uneventful postoperative course. The pathological diagnosis was mucinous cystadenocarcinoma of the pancreas with anaplastic carcinoma. Although the patient underwent postoperative adjuvant chemotherapy with gemcitabine and oral fluoropyrimidine (S-1), recurrence with peritoneal dissemination was detected 20 months following surgery and the patient succumbed to the recurrence 32 months following surgery. To the best of our knowledge, this is the first case report of MCN with anaplastic carcinoma of the pancreas in a Jehovah's Witness patient undergoing pancreatic surgery.