Advanced head and neck (H&N) tumors have a poor prognosis, and this is worsened by the occurrence of hypoxia and ischemia in the tumors. Ozonetherapy has proved useful in the treatment of ischemic syndromes, and several studies have described a potential increase of oxygenation in tissues and tumors. The aim of this prospective study was to evaluate the clinical effect of ozonetherapy in patients with advanced H&N cancer in the course of their scheduled radiotherapy. Over a period of 3 years, 19 patients with advanced H&N tumors who were undergoing treatment in our department with non-standard fractionated radiotherapy plus oral tegafur. A group of 12 patients was additionally treated with intravenous chemotherapy before and/or during radiotherapy. In the other group of seven patients, systemic ozonetherapy was administered twice weekly during radiotherapy. The ozonetherapy group was older (64 versus 54 years old, P = 0.006), with a higher percentage of lymph node involvement (71% versus 8%, P = 0.019) and with a trend to more unfavorable tumor stage (57% versus 8% IVb + IVc stages, P = 0.073). However, there was no significant difference in overall survival between the chemotherapy (median 6 months) and ozonetherapy (8 months) groups. Although these results have to be viewed with caution because of the limited number of patients, they suggest that ozonetherapy could have had some positive effect during the treatment of our patients with advanced H&N tumors. The adjuvant administration of ozonetherapy during the chemo-radiotherapy for these tumors merits further research.