Head and neck irradiation is the standard treatment of advanced oral/oropharyngeal cancer. The treatment has severe side effects such as mucositis, xerostomia, irradiation caries, trismus, and osteoradionecrosis. Side effects can lead to treatment discontinuation, infection, increased drug consumption, and increased duration of hospital admission and can have negative impact on the quality of life and overall survival. Furthermore, some of them (mucositis and xerostomia) affect almost every (>90%) patient. Since nearly two-thirds of oral/oropharyngeal cancers are diagnosed in advanced stage, one might conclude that the great majority of patients will be affected. However, these side effects can be prevented or at least reduced by proper oral/dental care. Therefore, every patient planned for head and neck irradiation should undergo dental evaluation before beginning of the treatment.