Head and neck cancers (HNC) are malignancies originating from the mucosa in the oral cavity, nasopharynx, oropharynx, hypopharynx and larynx. Unfortunately, the majority of patients with HNC have locally advanced disease at diagnosis and should, therefore, be treated with chemoradiotherapy (CRT) or with radical surgery followed by adjuvant (C)RT. Treatment of HNCs with (C)RT frequently results in serious and persistent impairments in physical and psychosocial functioning. In order to prevent worsening of a person's functioning at diagnoses and limit the physical impact of the treatments for HNC, a comprehensive supervised exercise program (CSEP) is needed early during treatment. There is a need to improve integration of exercise programs into HNC care with aim to help head and neck cancer patients regain physical, mental and social functioning. Currently, no program is available adapted to the specific needs of head and neck cancer patients, in particular during cancer treatment. The primary scientific objective is to examine the effectiveness of a comprehensive supervised exercise program, in addition to usual care, on health-related quality of life (primary outcome parameters) during treatment of head and neck cancer, compared to usual care only, up to 1 year after diagnosis. Secondary objectives entail gathering information on the effectiveness of the CSEP, in addition to usual care on secondary outcome parameter such as physical and mental functioning, activity level and participation level; to determine the feasibility of such CSEP (defined as at least 50% of eligible patients enrolling in the study and completing at least 50% of the planned intervention sessions) and possible barriers and facilitators for participating in a CSEP during head and neck cancer treatment.