A 73-year-old man was admitted with bloody stool. Duodenoscopy showed a hemorrhagic ulceration in the duodenum on the side opposite to the papilla of Vater. Abdominal CT demonstrated a well-defined hypervascular mass, adjacent to the lesion of the duodenum. Although as duodenal GIST was diagnosed, histologic examination for frozen sections during the procedure revealed tubular adenocarcinoma of the duodenum and pancreaticoduodenal lymph node metastasis of neuroendocrine carcinoma. He underwent a subtotal stomach-preserving pancreaticoduodenectomy. Clinicopathologically, the neuroendocrine carcinoma of the pancreaticoduodenal lymph node was considered to be metastasis from an unknown primary lesion.