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Neuroendocrine carcinomas from an unknown primary site are uncommon. The authors report on a case of neuroendocrine carcinoma in a perigastric lymph node (LN) with no primary site. A 52-year-old male patient with early gastric adenocarcinoma underwent treatment by endoscopic submucosal dissection, and, six months later, findings on a computed tomographic scan of the abdomen revealed a LN enlargement measuring 2.0 cm in the perigastric region. The patient underwent subtotal gastrectomy and regional LN dissection under a suggestive preoperative diagnosis of gastric adenocarcinoma with LN metastasis. However, microscopically, no residual tumor was found in the stomach, and the perigastric LN showed poorly differentiated neuroendocrine carcinoma (PDNEC). After an extensive workup, no primary site was identified. The patient also received four cycles of etoposide and cisplatin. Despite its extremely rare incidence, this case suggests that PDNEC of an unknown primary site is limited to a single site, and that resection should be considered in combination with chemotherapy.