PURPOSE: Millions of scars are formed annually with wide-ranging effects on the quality of life of the individual. Currently, there is no internationally validated, rigorously tested PRO measure (‘PROM’) that can be used to assess scar outcomes of all major etiologies in both children and adults. Nor, do we currently understand why patients may seek scar revision surgery. The purpose of this study is to describe the international field-test of seven clinics in four countries, the psychometric properties of the PROM, and the independent risk factors of patients requiring scar revision surgery. METHODS: Between March, 2017 and April, 2018 data were collected from 7 outpatient clinics in New Zealand, Chile, Canada, and the USA. Participants completed a questionnaire booklet with demographic and clinical questions as well as the preliminary SCAR-Q (Appearance, Symptom, and Psychosocial Impact). Rasch Measurement Theory (RMT) analysis was conducted examining item response options, item fit statistics, dependency, targeting, stability, and person separation index. In addition, Cronbach’s alpha and intraclass correlation coefficient were completed to examine reliability. In addition, a multivariable regression analysis was completed to examine independent risk factors for patients self-reporting the need for scar revision surgery. RESULTS: 773 patients were consented and 731 patients completed the survey results in full. Participants were aged 8–88 years with predominantly surgical scars (n=354, 48.4%), traumatic (n=199, 27.2%), and burn scars (n=184, 25.1%). Analysis led to the refinement of the SCAR-Q scales: Appearance, Symptoms, and Psychosocial Impact from 48 items to the final 29 items. RMT analysis showed ordered thresholds for response options, 25 items had fit residuals within the required range, and residual correlations were found only with one pair of items. Reliability was high, with Person Separation Index values of 0.90, 0.82, 0.84, Cronbach alpha values 0.96, 0.91, 0.95 and Intraclass Correlation Coefficient values of 0.92, 0.94. 0.88 respectively. Finally, having a health condition (OR 2.032; 0.944, 4.370), perceiving that one scars badly (OR 2.631, 1.195–5.792), a prior scar revision surgery (0.253; 0.127–0.672), and scoring poorly on the SCAR-Q Psychosocial Impact scale (OR 0.339; 0.171–0.672) were independent risk factors for reporting the need for future scar revision surgery. CONCLUSION: This RMT analysis showed that the 3 SCAR-Q scales performed well in this international, field-test sample, with good to excellent reliability. The SCAR-Q represents a rigorously developed PROM that can be used to evaluate scars in research, clinical care, and quality improvement initiatives. In addition, this study suggests that patients with the listed independent risk factors may require heightened attention and clinical care. These individuals may require more scar symptom management, psychosocial support in the case of social work or in severe cases a psychiatry referral, and/or scar treatment to help alleviate their appearance related concerns.