A 73-year-old man visited our hospital complaining of abdominal pain. An abdominal CT scan revealed diffuse wall thickening of the gallbladder with a gallstone. Urgent laparoscopic cholecystectomy was performed with the diagnosis of acute cholecystitis. Histopathological examination indicated adenocarcinoma with a small neuroendocrine carcinoma component invading the subserous layer. Additional gallbladder bed resection and lymphadenectomy were performed. The final pathological diagnosis was adenocarcinoma with NEC, pT2N0M0, pStage II . The patient is alive without any recurrence 7 months after the last surgery.