Sporadic desmoid-type fibromatosis (DTF) is a rare soft tissue tumour with an unpredictable clinical course. These tumours are incapable of metastasising, but their local aggressive tumour growth and tendency to recur locally can result in a substantial symptom burden. Measuring the impact of DTF on health-related quality of life (HRQoL) can be challenging due to the variable clinical presentation of the disease. Therefore, a HRQoL instrument assessing DTF-specific issues is needed. The QUALIFIED study aims to (1) pre-test a previously developed DTF-specific HRQoL tool (the DTF-QoL); (2) evaluate prevalence of HRQoL issues in adult DTF patients; and (3) identify subgroups at risk of impaired HRQoL. This study (NCT04289077) is an international, multicentre, cross-sectional, observational cohort study. Patients ≥ 18 years with sporadic DTF from the Netherlands and the United Kingdom will be invited to complete a set of questionnaires specifically composed for this patient group. Questionnaires will be completed using PROFILES (Patient Reported Outcomes Following Initial treatment and Long-term Evaluation of Survivorship). Analyses will include testing the psychometric properties of the DTF-QoL and evaluating the prevalence of HRQoL issues using the DTF-QoL, EORTC QOL-C30 and EQ-5D-5L, among other questionnaires. This study will provide insight into HRQoL issues experienced by patients with DTF. Awareness of these issues and the implementation of the DTF-QoL in research and clinical practice can help to improve overall HRQoL and to provide personalised care.