We report herein the case of a 46-year-old-man with small cell neuroendocrine carcinoma (NEC) concomitant with large villous adenoma of the rectum, who underwent abdominoperineal resection with regional lymphnode dissection. The resected specimen was histologically found to contain a small lesion of NEC confined to the submucosa in the large adenoma. A computed tomography scan done 4 months postoperatively revealed recurrences in the liver, lymph nodes, and bone. Therefore, two cycles of sequential intravenous combined chemotherapy with standard doses of cisplatin and 5-fluorouracil (5-FU) were administered, after which the size of each tumor decreased remarkably. Nevertheless, the patient died 8 months after the operation. As there was a fair response of this tumor to the combined chemotherapy of cisplatin and 5-FU, this regimen against NEC of the colon and rectum should be given consideration.