Background: Oral mucositis (OM) is a frequent inflammatory toxic reaction during the treatment of head and neck cancer (HNC) with radiation therapy and/or chemotherapy. It can provide malnutrition, hospitalization, interruption in cancer treatment and compromise the quality of life of the patient. Objective: To evaluate the rate of suspension of radiotherapy, associated or not with chemotherapy, before and after the implementation of evidence, in adults and elderly with HNC. Method: The rates of suspension of radiotherapy before and after implementation were compared, with qualitative variables represented by frequencies and percentages and quantitative variables through position and dispersion measures. For the implementation of evidence, we followed the seven steps of the JBI evidence implementation method, based on the audit and feedback approach, using the tools JBI Practical Application of Clinical Evidence System (PACES) and Getting Research into Practice (GRiP). Eight audit criteria were used for evaluation, prevention and management of OM, inserted in the JBI PACES program, plus a criterion of the MASCC/ISOO Guideline. The study was approved by the Research Ethics Committee of Unicamp under the number CAAE: 47636621.0.0000.5404. Results: 21 patients were included in the pre-implementation audit of evidence; 90.48% had OM; 47.61% had their radiotherapy treatment suspended, 42.86% (mean: 12, SD 8.87) as a result of OM and its complications. The median of suspension was 7 days, with a minimum of 5 days and a maximum of 28 days. In the post-implementation audit of evidence, 19 patients were included, 47.37% had OM, 15.79% (mean: 14, SD 7.00) had their radiotherapy treatment suspended, none due to OM and its complications. Conclusions: OM did not provide interruption in radiotherapy treatment after the implementation of evidence, suggesting a positive effect of best practices related to the prevention and management of OM. The implications for the practice: Radiotherapy when performed without suspensions due to OM and its complications increases the chances of success in the treatment of patients with HNC and contributes to improving the quality of life.