Following radiotherapy of malignant head and neck tumours, tooth damage is observed in many cases, which is frequently referred to as "radiation caries". This is not the immediate result of radiation, but has a number of causes. The damage to the salivary glands caused by radiation leads to xerostomia, which affects the self-cleaning capacity in the mouth. As a result of the very painful mucositis which occurs during the course of radiotherapy as well as the restricted mastication caused by the operation, patients prefer a soft diet, which in turn promotes plaque formation. The acidogenic coating causes erosion of the enamel. If preventive measures are not taken, all of the teeth can be completely destroyed within a short time. All efforts should be made to prevent this from happening, particularly in young patients who have undergone curative radiotherapy. This should include intensive fluoride treatment and meticulous oral hygiene.