Background: The incidence of OPSCC has increased dramatically in the last 15 years. The standard treatment for early stage disease is either surgery or radiotherapy, both with comparable high tumor control rates but with different side effect profiles and technical constraints. Treatment choice is generally based on expert or center experience. It is still unclear whether they differ in terms of functional outcome. To clarify this, we proposed a randomised trial with the primary objective to assess and compare the patient-reported swallowing function over the first year after randomisation to either IMRT or TOS among patients with early stage OPSCC. Clinician and patient-reported outcomes will be used to assess treatment. Methods: This is a phase III randomised trial (NCT02984410) that will primarily assess the MD Anderson Dysphagia Inventory (MDADI) score reported by the patients at months 4.5, 6, 9, and 12 after randomisation. MDADI is composed of 19 questions on emotional, functional, and physical aspects, all related to swallowing, wherein scores range between 20 (poorest function) and 100 (best function). BEST OF is powered to detect a clinically significant difference in MDADI score at each of these time points: 4.5, 6, 9, and 12 months with a planned sample size of 170 patients. Key secondary endpoints include treatment response at 6 months after randomization, oncologic outcomes at year 1 and 5, toxicities based on CTCAE, quality of life (QOL) based on QLQ-C30 and HN43 and out-of-pocket costs. QOL domains will be ranked based on patient's priorities. Eligible cases are resectable T1 or T2, N0, M0 OPSCC assessed by a multidisciplinary team. The EORTC quality assurance program (QA) for surgery and pathology (SURCARE) and radiotherapy (RTQA) was implemented in the study. This integrated QA will be the model for future EORTC Head and Neck Cancer trials. BEST OF was opened for recruitment since December 2017 in Belgium and Switzerland and will soon open in France, UK, Germany, Poland, Italy and Portugal through a collaboration with EORTC HNCG and ROG, SAKK, NCRI, GORTEC, and IAG-KHT. Clinical trial information: NCT02984410