Cisplatin is an essential platinum agent that has been widely used for various solid malignant tumors. However, it has a problem in cisplatin-induced hearing-loss (CIHL). Cisplatin-induced hearing-loss involving the speech frequencies (500-2,000 Hz) is usually induced by cumulative doses of >400 mg/m 2. Children are more susceptible to ototoxicity from cisplatin than adults. 1 Recently, some clinical trials indicated that sodium thiosulfate (STS) has a potential otoprotective effect. 2,3 However, in patients with disseminated disease, those who received STS showed lower overall survival than patients in the control group. 3 The expert panel made a strong recommendation for STS administration in patients with nonmetastatic hepatoblastoma, a weak recommendation for STS administration in patients with other non-metastatic cancers, and a weak recommendation against its routine use in metastatic cancers. 4 We report the case of a patient with medulloblastoma who was monitored by periodic serial evaluations for ototoxicity and in which the progression of CIHL was prevented by STS. A 9-year-old boy presented with a 1 month history of headache and nausea. A physical examination revealed no other neurological signs. Magnetic resonance imaging (MRI) of the brain revealed a tumor arising from the cerebellum with gadolinium enhancement. The tumor was completely resected, and was pathologically diagnosed as medulloblastoma, classic, non-WNT-activated subtype. Craniospinal radiation (23.4 Gy) with a posterior fossa boost of 32.4 Gy was performed. Weekly vincristine was administered during radiotherapy to the posterior fossa. After the completion of radiotherapy, sequential adjuvant chemotherapy consisting of cisplatin,