Turcot syndrome is characterized by the concurrence of a primary neuroepithelial brain tumor and multiple colorectal polyposis. We report a case of a 24-year-old woman diagnosed with Turcot syndrome. At first, the patient was diagnosed as having a medulloblastoma after a tumorectomy of the 4th ventricle mass. The patient underwent radiotherapy and chemotherapy. After high-dose chemotherapy, neutropenic fever and severe mucositis developed. For an evaluation of the persistent hematochezia and diarrhea, a colonoscopy was performed. It revealed pseudomembranous colitis and multiple polyps in the entire colon. According to the family history, her father had undergone a total colectomy due to colon cancer and polyposis of the entire colon. Her brother also was found to have multiple polyps in the colon by a colonoscopy. The patient was diagnosed with Turcot syndrome.