BACKGROUND Neuroendocrine neoplasms (NENs) originate from cells of the endocrine and nervous systems, and they are rarely encountered in colorectal cases with no specific symptoms. The incidence and prevalence of NENs of the large bowel are increasing. Malignant colonic types are known to have poor diagnosis. The mean age of colonic NENs is the seventh decade, and the risk of NENs is increased 4-fold with affected first-degree family members. CASE REPORT A 57-year-old male patient presented to our Emergency Department with a 5-day history of severe generalized abdominal pain associated with worsening abdominal distension, history of night sweats, and weight loss. A CT scan of the abdomen and pelvis demonstrated a large heterogeneously enhancing neoplastic mass lesion involving the splenic flexure of the colon surrounded by fat stranding with a small contained leak, in addition to multiple metastatic hypodense focal hepatic lesions. Multiple lymph nodes under 1 cm in size were also noted. The patient underwent exploratory laparotomy, subtotal colectomy, ileostomy creation, and washout. The histopathological exam revealed high-grade invasive colonic neuroendocrine carcinoma, which was pT4N2bM1c, while the peritoneal lesion was metastatic carcinoma. The patient was then referred to the multidisciplinary tumor board. CONCLUSIONS Unusual presentation of neuroendocrine tumors is shown to be expected. Since colorectal NECs are rare, highly aggressive diseases and usually discovered very late, individualization of management, as well as additional research, is required.