Colorectal cancer (CRC) has a propensity to metastasize to the liver, lungs and regional abdominal lymph nodes, but rarely to the bone marrow. A 60-year-old man presented to the National Hospital Organization Kyushu Cancer Center with a 4-week history of persistent lower back pain, anorexia and difficulty defecating. Complete blood count revealed severe thrombocytopenia and erythroblastosis, suggesting a hematological malignancy. However, the bone marrow examination demonstrated involvement by a moderately to poorly differentiated adenocarcinoma, but no hematopoietic abnormalities. A computed tomography scan revealed thickening of the wall of the sigmoid colon, with para-aortic, hilar, mediastinal and supraclavicular lymphadenopathy. The patient was thus diagnosed with sigmoid colon adenocarcinoma with lymph node and bone marrow metastasis. Modified FOLFOX6 was promptly initiated, with concurrent therapy for disseminated intravascular coagulation (DIC). An increased number of thrombocytes was observed on day 6. After 3 cycles of treatment, the patient recovered from DIC and the levels of serum carcinoembryonic antigen and cytokeratin 19 fragment were decreased. Tumor biopsy during colonoscopy following recovery from DIC demonstrated poorly differentiated adenocarcinoma with mucin production, without mutations in the RAS, BRAF or PIK3CA genes, and a cytokeratin (CK) 7-negative, CK20-positive phenotype. The patient has been treated with chemotherapy for 150 days without disease progression. However, the efficacy of chemotherapy for rarely encountered bone marrow metastasis from CRC is poor. The present case was favorably maintained on chemotherapy and survived for 10 months.