Mediastinal lymph node metastasis from colorectal cancer is rarely seen. We herein report on a 74-year-old man who was hospitalized with multiple brain metastases and mediastinal lymph node metastasis from an adenocarcinoma of the sigmoid colon. A preoperative brain magnetic resonance image showed multiple brain tumors, and a chest computed tomography (CT) scan indicated a mediastinal tumor. CT-guided aspiration biopsy cytology of the mediastinal tumor showed metastatic adenocarcinoma from a digestive tract tumor. Barium enema and sigmoid colonoscopy showed that the cancer was located in the sigmoid colon. Laparoscopic assisted sigmoidectomy with lymph node dissection was performed. Pathological findings of the specimen showed a moderately differentiated adenocarcinoma that invaded to the subserosa, but no evidence of lymph node metastasis was found. The patient was discharged 3 weeks after the operation and died 3 months later.