Disseminated carcinomatosis of the bone marrow is caused by metastasis to the bone marrow and can cause disseminated intravascular coagulation (DIC), leucoerythroblastosis, and microangiopathic hemolytic anemia (MHA). The prognosis of this syndrome is poor. We report herein two rare cases of disseminated carcinomatosis of the bone marrow in association with prostate cancer. Case 1 involved a 61-year-old man admitted to our department with elevated prostate-specific antigen (PSA) levels. Prostate biopsy revealed prostate cancer, and imaging studies were performed. Under a diagnosis of prostate cancer (T3N1Mx), the patient was treated using hormonotherapy, but died 2 months after admission due to gastrointestinal bleeding of unknown cause, refractory DIC, and cachexia. Bone marrow biopsy after his death revealed metastasis of the prostate cancer to the bone marrow. Case 2 involved a 68-year-old man admitted to our department with gross hematuria. Cystoscopy revealed non-papillary tumor in the prostatic urethra. Transurethral biopsy was performed and histology identified prostate cancer. Treatment was initiated with hormonotherapy and zoledronate. After 8 months, he complained of general fatigue and blood testing identified anemia and thrombocytopenia. Bone marrow biopsy revealed adenocarcinoma in the bone marrow. Alternative androgen therapy and chemotherapy with docetaxel was started, and the patient recovered from pancytopenia and general fatigue.