123 7 Introduction Head and neck cancer (HNC) is the seventh most common cancer worldwide, most often caused by alcohol and/or tobacco use, or the human papilloma virus (HPV).1 Treatment options for HNC include surgery, radiotherapy (RT) and chemoradiotherapy (CRT). The use of high-intensity radiation treatment regimens have resulted in improved survival, but the prevalence of patients suffering from side effects of treatment has increased as well.2 Patients may suffer from e.g., tissue fibrosis, osteoradionecrosis, xerostomia, or dysphagia. Dysphagia may occur in up to 44% of patients treated with RT and up to 84% of patients treated with surgery.3,4 Swallowing function may be impaired due to a number of normal tissue changes such as edema, neuropathy, fibrosis, and mucositis.5 While edema and mucositis disrupt normal swallowing function during treatment, they substantially improve after treatment in the majority of patients. In contrast, neuropathy and fibrosis of the swallowing musculature may develop or persist long after completion of treatment.5 Swallowing dysfunction can lead to complications such as malnutrition, aspiration and subsequent pneumonia, which may depend on tumor stage, sub-site of the tumor, age, and treatment modality.6,7 RT may result in a large dose delivery to critical structures necessary for normal deglutition, such as the base of tongue, supraglottic larynx, soft palate, cricopharyngeal muscles and pharyngeal constrictor muscles.8 Chemotherapy may also have an effect on swallowing function, and it may lead to various side effects such as nausea, vomiting, neutropenia, generalized weakness and fatigue.5 Swallowing problems that occur after surgery vary with tumor site and size of resection, and type of reconstruction.9 In order to reduce the risk of swallowing dysfunction before and after curative treatment for HNC, it is important to identify factors associated with swallowing dysfunction. Therefore, the aim of this prospective study was to identify factors associated with swallowing dysfunction in patients with HNC, before, and 3, 6, 12, and 24 months after treatment. It was hypothesized that especially treatment modality, tumor site, and tumor stage will have a significant impact on swallowing function after treatment. Materials and methods Patients were included by convenience sampling when they were 18 years or older, were diagnosed with oral, oropharyngeal, hypopharyngeal, or laryngeal HNC and were treated with a curative intent at the University Medical Center Utrecht (UMCU), the Netherlands between September 2014 and June 2018. Patients with recurrent or residual disease, cognitive impairments, and patients having trouble understanding or reading the Dutch language were excluded. All patients signed written informed consent before participation.