Colonic neuroendocrine cell carcinoma (NEC), which is a rare subtype of colon epithelial neoplasm, has been reported to show extremely aggressive characteristics with a 1-year survival rate of 20%. We report herein a resected case of NEC that manifested bacterial sepsis due to sigmoidovesical fistula. Staged surgery consisted of resecting the sigmoid colon and part of the bladder four weeks after construction of an ileostomy to alleviate septic shock. The resected specimen was histologically diagnosed as NEC invading the wall of the urinary bladder with metastasis to the regional lymph nodes. The patient underwent four cycles of FOLFOX after surgery for additional treatment of residual metastatic lymph nodes around the abdominal aorta diagnosed preoperatively. Although the patient showed stable disease measured by computed tomography scan for the first three months after surgery, he rejected additional chemotherapy thereafter, and died ten months after the initial admission due to progression of residual tumor in the urinary bladder as well as the lymph nodes. This is the first case report describing colonic NEC manifesting perforation into the urinary bladder. Although the optimal chemotherapeutic regimen for colonic NEC has not yet been established, FOLFOX may be one of the choices.