Valid patient-reported outcome (PRO) measures are required to evaluate alopecia areata (AA) treatments.To develop a content-valid and clinically meaningful PRO measure to assess AA scalp hair loss with scores comparable to the 5-response level AA Investigator Global Assessment (AA-IGA).A draft PRO measure was developed based on input from 10 AA clinical experts. The PRO measure was cognitively debriefed, modified, and finalized through two rounds of qualitative semi-structured interviews with patients with AA who had experienced 50% scalp hair loss. Data were thematically analysed.Adults (Round1: n=25; Round2: n=15) and adolescents aged 15-17 (Round1: n=5) in North America participated. All patients named scalp hair loss as a key AA sign/symptom. Patients demonstrated the ability to self-report their current amount of scalp hair using percentages. In Round1 not all patients interpreted the measurement concept consistently; therefore, the PRO was modified to clarify the measurement concept to improve usability. Following modifications, Round2 patients responded without difficulty to the PRO measure. Patients confirmed that they could use the 5-level response scale to rate their scalp hair loss (No missing hair, 0%; Limited, 1-20%; Moderate, 21-49%; Large, 50-94%; Nearly all or all, 95-100%). Almost all patients deemed hair regrowth resulting in 20% scalp hair loss a treatment success.The Scalp Hair Assessment PRO is a content-valid, clinically meaningful assessment of distinct gradations of scalp hair loss for evaluating AA treatment for patients with 50% hair loss at baseline.