The term comorbidity stands for disease processes that co-exist and are not related to the index disease being studied. Comorbidity in cancer has been shown to be a major determinant in treatment selection and survival. Patients with head and neck cancer can have significant comorbidity owing to the high incidence of tobacco and alcohol abuse. No studies to date have addressed this problem in head and neck cancer patients in the United Kingdom. The applicability of the adult comorbidity evaluation – 27 index (ACE-27) and the Charlson index (CI) to assess the comorbidity burden by retrospective notes review is studied here. Retrospective data collection and completion of a comorbidity index in a United Kingdom setting is feasible. We conclude that the pre-assessment visit is a useful time to record comorbidity and as a significant amount of information required for grading relates to historical items, this is best done using a self-administered patient questionnaire.