Adenoendocrine cell carcinoma of the gallbladder is an uncommon form of cancer. We treated a 36-year-old woman who came to us with a chief complaint of abdominal pain. The abnormality was diagnosed to be a tumor-like mass in the gallbladder, and adenomyomatosis of the gallbladder was strongly suspected. A laparoscopic cholecystectomy was successfully performed, and the histopathological finding was adenoendocrine cell carcinoma of the gallbladder. The tumor cells of the small round cell carcinoma partly stained positively for synaptophysin, neuron-specific enolase, and CD 56, while adenocarcinoma cells showed positive reactions to keratin, which was thus suggestive of adenoendocrine cell carcinoma. The patient is alive and doing well at 12 months after the treatment.