We present a successfully treated case of mixed ductal-endocrine carcinoma of the pancreas complicated by right renal cell carcinoma. The patient had no symptoms, and laboratory data were close to the normal range. Enhanced computed tomography demonstrated a marked enhanced tumor, which appeared to be an endocrine tumor, at the pancreas uncus. We performed pyrolus-preserving pancreaticoduodenectomy, regional lymph node resection, and right nephrectomy. Histologically and immunohistochemically, the pancreas tumor had both a ductal (exocrine) and an endocrine component. The renal tumor was a typical clear cell carcinoma. A diagnosis of synchronous double cancer was made. As demonstrated in previously published reports, this type of mixed tumor has malignant potential for invasive ductal carcinoma. We propose that mixed ductal-endocrine carcinoma of the pancreas should be treated by surgical resection with a sufficient surgical margin and regional lymph node resection to improve the patient's prognosis.