Conclusions: Intra-arterial high-dose cisplatin chemoradiation (CRT-IA) with sodium thiosulfate (STS) causes relatively less severe cisplatin ototoxicity than intravenous cisplatin chemoradiation without STS (CRT-IV). The results of this study also suggest that early detection of ototoxicity is possible by testing the hearing loss at ultra-high frequencies. Objectives: To investigate protective effects of STS against cisplatin ototoxicity. Methods: Between 2011 and 2013, 18 patients with head and neck carcinomas were treated with intra-arterial infusions of high-dose cisplatin (range 100-180 mg/body, mean 111 mg/body; range 2-5 courses, mean 3.6 courses) and systemic administration of cisplatin (range 66-185 mg/body, mean 130 mg/body; range 1-3 courses, mean 2.6 courses) and concurrent radiation therapy (range 60-70 Gy, mean 69 Gy). Cisplatin was neutralized by STS in CRT-IA but not in CRT-IV. Results: Intra-arterial infusion in the high-dose cisplatin group caused significant hearing loss at ultra-high frequencies of 10 and 12 kHz (p = 0.028, 0.039, respectively), whereas the group receiving systemic administration of cisplatin had significant hearing loss at high frequencies of 8 and 10 kHz (p = 0.016, 0.027, respectively).