Introduction and aim of the work: Oral mucositis (OM) occurs in more than 95% of patients irradiated in the head and neck area and is one of the most difficult to tolerate side effects. OM represents inflammation accompanied by painful ulcerations in the oral cavity, disrupting its function and preventing basic functions such as eating, swallowing, and speaking. It occurs at the end of the first week of RT and lasts for several weeks after stopping. The intensity of OM can sometimes lead to the interruption of RT. The aim of this thesis was to determine the occurrence and characteristics of OM in patients with head and neck cancer, as well as the involvement of dentists/oral medicine specialists in the treatment of such patients. Respondents and procedures: For the purposes of this thesis, a unique survey questionnaire was created with questions that are directly or indirectly related to the issue of OM. The questionnaire was completed by 30 patients with a history of head and neck cancer who were irradiated and/or receiving chemotherapy. Results: 22 patients developed OM. The largest number of patients developed the third degree of OM, that is, they could only consume liquid food. The largest number of patients developed OM up to ten days after the start of radiotherapy/chemoradiotherapy. In the largest number of subjects, OM lasted for two weeks after cessation of radiotherapy/chemotherapy. Ten patients were treated by OM according to the instructions of an oral medicine specialist, eight according to the instructions of a specialist responsible for the underlying disease, and four were not treated by OM at all. The most commonly used agent is a gel based on polyvinyl pyrrolidone (Gelclair). Conclusion: Although OM is the most common unwanted side effect of radiation and chemotherapy in head and neck cancer, dentists and oral medicine specialists, as the best experts in the prevention and treatment of OM, are still not sufficiently involved in the oncology team.