Mucositis is a painful, ulcerative inflammation that occurs due to the cytotoxic effect of chemotherapy and radiotherapy on the epithelial cells of the mucosa and affects the mucosa of the gastrointestinal system, which includes the mucous membranes of the mouth and throat. It is most commonly presented as erythema, atrophy, or ulceration of the mucosa. It occurs in almost all patients receiving radiation therapy of the head and neck, in 20-40% of patients on chemotherapy and 60-85% of patients undergoing hematopoietic stem cell transplantation. Mucositis develops a few days after the start of therapy, usually between the first and second week, lasts the entire duration of the therapy and stops two to four weeks after the end of therapy. Data from the literature show that 19% of patients treated with chemotherapy and radiation of the head and neck area were hospitalized due to the development of severe oral mucositis. Consequently, antineoplastic therapy delayed until the condition improves. The quality of life is reduced; poorer prognosis of the underlying disease is given, and the cost of treating the patient increased. It is crucial to inform the patient on this possible side effect of cancer therapy and on the available treatments that will alleviate the symptoms and allow continuous treatment of the underlying disease, for optimal therapeutic effect.