Abstract: Objective: Oral mucositis is one of the most profound toxicities during (chemo)radiotherapy for head and neck cancer, impacting a patient's quality of life. To measure the effect of oral mucositis on one's quality of life, the use of patient-reported outcome measures is of utmost importance. Since Dutch-validated patient-reported outcome measures assessing the impact of oral mucositis are lacking, the aim of this study was to translate the Oral Mucositis Weekly Questionnaire-Head and Neck Cancer into Dutch and to validate this version. Methods: The Oral Mucositis Weekly Questionnaire-Head and Neck Cancer was translated according to the internationally described crosscultural adaptation process. Thirty-five patients with head and neck cancer were asked to complete the Dutch version of the Oral Mucositis Weekly Questionnaire-Head and Neck Cancer, together with the Functional Assessment of Cancer Therapy and the Swallowing Quality-ofLife Questionnaire for 5 times during the first 5 weeks of chemoradiotherapy. The Toxicity criteria of the Radiation Therapy Oncology Group/ European Organization for Research and Treatment of Cancer was completed by the radiation oncologist at the same time points. Factor analysis was done for psychometric validation and reliability was tested using Cronbach's alpha. Convergent validity and discriminant validity were calculated and clinical validity was assessed. Results: Ninety-one percent of the questionnaires were completed. Internal consistency was high, after removing items 1, 2, and 4F. Testretest reliability was high, and convergent validity and discriminant validity were demonstrated. The Dutch version of the Oral Mucositis Weekly Questionnaire-Head and Neck Cancer can successfully detect differences in the impact of oral mucositis and is sensitive to detect changes in time. Conclusion: The Dutch version of the Oral Mucositis Weekly Questionnaire-Head and Neck Cancer is a valid and reliable instrument to assess the impact of oral mucositis in patients with head and ...