Cystadenocarcinomas arc rare tumors of Ihe'pancreas. They are half as common as their benign counterpart–the cystadenoma. A review of 21 cases, including eight reported since 1963, revealed that most patients presented with upper abdominal pain and a large palpable upper abdominal mass. All patients had evidence of malignant degeneration occurring in a mucous cystadenoma. None had evidence of a serous cystadenoma. Grading revealed a predominance of low-grade tumors: 20 of the 21 lesions were grade 1 or 2. Cystadenocarcinomas were slightly more frequent in the head of the pancreas. Four patients had metastasis. Complete excision by distal or total pancreatectomy or Whipple pancreaticoduodenectomy is recommended. The five year survival after complete excision is 68%, and for patients with grade 1 lesions, and five year survival is 64%.