PURPOSE: The aim of this study was to review our experience with neuroendocrine carcinoma (NEC) of the colon and rectum to highlight the clinical and pathological characteristics in this relatively uncommon malignancy. METHODS: From December 1995 to December 2006, 11 patients with NEC were identified from our database of 6,143 colorectal cancer patients (0.18%), which does not include carcinoid tumors. The pathology was retrospectively reviewed and the tumors were categorized as pure NEC, including well-differentiated NEC (n=3), poorly-differentiated (n=3) and mixed endocrine/exocrine tumor (n=5) on the basis of the histology and immunohistochemical findings. RESULTS: The mean age of the patients was 57 yr (range, 37 to 69 yr). The tumors were located as follows: 8 in the colon and 3 in the rectum. The diagnosis of NEC was suggested preoperatively from the tissue biopsy in 2 of 9 patients (22.2%). The tumors were advanced at the time of diagnosis, with American Joint Committee on Cancer Stage III (n=7) and Stage IV disease (n=4). Most tumors stained positive by immunohistochemistry for neuroendocrine markers, including synaptophysin (7/9, 77.8%); however, chromogranin was expressed in 4 of 9 NEC tumors (44.4%). Metastatic disease was detected at the time of diagnosis in 36.4% (4/11) of the patients. The median survival for NEC was 16 mo (3.6-67.4 mo), and for pure NEC and mixed endocrine/exocrine tumor was 4.1 mo and 23.6 mo, respectively. CONCLUSION: NEC had distinctive cytoarchitectural features and was often immunoreactive for neuroendocrine markers. Our findings showed that pure NEC had aggressive behavior and a poor prognosis.