BackgroundMycosis fungoides (MF) and Sézary syndrome (SS) are common subtypes of cutaneous T‐cell lymphoma that primarily affect the skin but may spread to the lymph nodes, viscera and blood. The symptom burden may compromise health‐related quality of life (HRQL). The phase 3 MAVORIC study (ClinicalTrials.gov identifier NCT01728805) in patients with relapsed/refractory MF/SS reported improved HRQL with mogamulizumab compared with vorinostat.ObjectivesUse baseline (pre‐treatment) data from the MAVORIC study to describe the symptom burden of MF/SS and identify characteristics associated with worse HRQL.MethodsData were from 372 adults with stage IB–IVB histologically confirmed relapsed/ refractory MF or SS. Associations between demographic and medical history variables and worse HRQL (Skindex‐29, ItchyQol and Functional Assessment of Cancer Therapy – General [FACT‐G]) were determined by regression models.ResultsIn the cohort of 372 adults, 70% were white; 42% were female; mean age was 63 (SD 13.0) years. Fifty‐five per cent had MF and 45% had SS; 77% had advanced (stage IIB–IV) disease, involving the skin in all patients and the blood and/or nodes in 66%. HRQL scores showed impairment versus normative means (where available), with the greatest impact on Symptoms and Emotions in the Skindex‐29, Functioning in the ItchyQol, and Functional Wellbeing in the FACT‐G. In regression analysis, worse HRQL across all domains and total score was associated with being female and younger, worse mSWAT score and worse itch for the Skindex‐29 (n = 352), and being female, younger, Black/African American, worse performance status and worse itch for the ItchyQol (n = 369). Associations across domains and total score were not found for the FACT‐G. Associations between domains and demographic/medical history were seen for all instruments.ConclusionsThe symptoms of advanced MF/SS compromise all HRQL domains. Treatment goals and therapeutic choice should be informed by individual patients' disease burden.