Rectal carcinoids comprise 12.6% of all carcinoid tumors and represent the third largest group of the gut carcinoids. A 64-year-old woman was diagnosed as high-grade neuroendocrine carcinoma. She had liver, bone, and bone marrow metastasis. Carcinoid syndrome was diagnosed due to diarrhea, nausea, vomiting, tachycardia, and high level of 24-hour urinary 5-hydroxyindoleacetic acid (160 mg/24 hours). No response was obtained by octreotide treatment. Rectal carcinoid tumors usually show favorable prognosis; however, poorly differentiated tumors might have unusually aggressive behavior and resistance to treatment. Bone marrow involvement might be a poor prognostic factor in carcinoid tumor as has been the case in many other tumors.