Primary small cell neuroendocrine carcinoma of adrenal gland Abstract Neuroendocrine tumors are an extremely rare form of retroperitoneum tumor. A 79-year-old man presented with abdominal pain. Computed tomography and magnetic resonance imaging revealed a 51 × 36 mm mass in the left adrenal gland. Gastrofiberscopy, colonfiberscopy and positron emission tomography were performed and showed no lesions or other malignancies. Endocrine tests were normal. Two months later, the mass had grown to 68 × 52 mm. Suspecting a malignant tumor, we performed laparoscopic adrenalectomy. Histopathological diagnosis revealed the tumor was small cell neuroendocrine carcinoma. No other malignancies were revealed, so we diagnosed primary small cell neuroendocrine carcinoma of adrenal gland. To our knowledge, this is only the third report in English of primary small cell neuroendocrine carcinoma of the adrenal gland and the first report that is confined to the adrenal gland. Adrenal masses are often misdiagnosed as adenoma; however, we need to raise awareness of the potential for malignant adrenal tumors such as the rarer small cell neuroendocrine carcinoma.