77 5 Introduction Head and neck cancer (HNC) is the seventh most common cancer worldwide, most often caused by alcohol and tobacco use, or the human papilloma virus (HPV).1 Treatment options for HNC (e.g., oral, pharyngeal or laryngeal cancer) include surgery, radiotherapy (RT) and chemoradiotherapy (CRT). After treatment, patients may suffer from tissue fibrosis, osteoradionecrosis, xerostomia, or dysphagia. Deterioration in oral functioning (such as mastication, swallowing, saliva production, taste, dental condition, and speech) can result in complications such as malnutrition, dehydration, aspiration and subsequent pneumonia. Within the first year after radiotherapy, approximately half of the HNC survivors experience difficulties with oral functioning, and unmet survivorship needs are common.2 HNC survivors may experience psychosocial problems such as social isolation and depression, which decreases a person’s quality of life (QoL).3-5 To determine oral functioning before and after treatment, objective and subjective measures can be used. Objective measurements are based on how well a person can perform a task, irrespective of what they experience while performing the task. They are based upon an accurate representation of the world, and are therefore unbiased because they record only what is observed, without adding or taking away from the observation.6,7 A person’s subjective evaluation depends on individual values and priorities, which may differ between persons and even within persons. This subjective evaluation, or patientreported outcome measure (PRO), is based on what people actually experience, and is increasingly being integrated in routine clinical practice.8,9 It has shown to contribute to improved communication, patient satisfaction, earlier detection of problems and subsequently earlier referral, and more efficient use of health services.8 In order to develop strategies to reduce side-effects of oncological treatment, it is important to know the relation between the patients’ subjective evaluation of his/her oral functioning and the objective function of the various organs involved. In previous research, multiple studies looked at this relation between objective and subjective measurements, especially comparing swallowing outcomes.10-13 However, many different measures have been used, and there is a lack of consensus about a preferred method to measure swallowing performance.10 In addition, most studies focus only on one part of oral functioning, or at one point in time. Therefore, in this paper, objective measures and PROs are compared for three main oral functions (mastication, swallowing, and salivary flow), using the same methodology in a large group of patients at different time points. To measure more aspects of oral functioning in time, and in particular masticatory performance, dysphagia and xerostomia, different tests can be used. Objective masticatory performance can be measured with, for example, comminution methods, sieving and optical