Background Hidradenitis suppurativa (HS) is a chronic inflammatory disease. The HS core outcome set calls for a patient global assessment (PtGA). Objectives To assess the validity, reliability and responsiveness of a candidate single‐item PtGA for HS‐specific health‐related quality of life (HRQoL). Methods Cognitive debriefing interviews were conducted with patients with HS in Denmark and the USA. A cross‐sectional observational study was done with adults with HS in the USA and Denmark. Candidate PtGA item, demographic items and multiple patient‐reported scales – the Hidradenitis Suppurativa Quality of Life (HiSQOL), Dermatology Life Quality Index (DLQI) and numerical rating scale (NRS) for pain – were concurrently administered to evaluate convergent and known‐groups validity. Scales with a single‐item assessment of change were readministered 24–72 h later, to evaluate reliability and responsiveness. Results After cognitive debriefing, the candidate PtGA for HS‐specific HRQoL was finalized with five response levels. Convergent validity of the PtGA was supported by significant correlations with HiSQOL score r = 0·79, 95% confidence interval (CI) 0·75–0·82 and DLQI (r = 0·78, 95% CI 0·74–0·82). The PtGA displayed known‐groups validity with DLQI score bands based on significance of an anova (P < 0·001). Good test–retest reliability was supported by the intraclass correlation coefficient (0·82, 95% CI 0·78–0·85) for those who reported stable HS. Responsiveness was assessed by differences in PtGA score against a patient‐reported assessment of change, which showed significant differences towards improvement. Conclusions The single‐item PtGA exhibits reliability, validity and responsiveness in assessing HS‐specific HRQoL in HS, making it a good provisional tool for HS clinical research. What is already known about this topic? Hidradenitis suppurativa (HS) can have a large negative impact on health‐related quality of life (HRQoL). Patient global assessments are useful in eliciting important aspects of the patient’s perspective on an individual basis. Few studies have developed and investigated the measurement properties of a patient global assessment (PtGA) item for HS. What does this study add? This study describes the development, validation and psychometric properties of a PtGA item for HS. This PtGA item for HRQoL shows promise with its validity and reliability, allowing for its further development as a clinical research tool. What are the clinical implications of this work? The PtGA item can now be investigated longitudinally in a treated population to further elucidate the responsiveness, minimally important change and score bands.