Choroid plexus carcinoma (CPC) is a malignant tumor with a strong tendency to spread along the cerebrospinal fluid pathway. There is no standardized chemotherapy protocol for this rare tumor. We report a 38-year-old man with CPC in the lateral ventricle with obstructive hydrocephalus. Because of the poor demarcation between thalamus and fornix, subtotal tumor resection was performed. Postoperative spine magnetic resonance (MR) image revealed whole spinal axis dissemination. After diagnosis of CPC, the patient was treated with whole ventricular and spine radiation concomitant with temozolomide chemotherapy, although the O(6)-methylguanine-DNA methyltransferase (MGMT) promoter was found to be unmethylated. Although MR images revealed transient stable disease during adjuvant therapy, tumor progression was depicted after four cycles of temozolomide therapy. We discuss the ineffectiveness of adjuvant temozolomide therapy for CPC in connection with O(6)-methylguanine-DNA methyltransferase promoter methylation.