OBJECTIVES:  PAH-SYMPACT^® is a patient reported outcome (PRO) instrument developed based on interviews with patients with pulmonary arterial hypertension (PAH) and following the FDA's PRO guidance. Its psychometric characteristics are being evaluated using data from the phase IIIb PAH SYMPHONY study. After item reduction, the final instrument consists of 11 symptom items across 2 domains (cardiopulmonary and cardiovascular symptoms) and 11 impact items across 2 domains (physical impact and cognitive/emotional impacts). The objective of this analysis was to evaluate the psychometric properties of the PAH-SYMPACT^® domain scores. METHODS:  In SYMPHONY, patients completed generic and disease-specific questionnaires, while clinicians provided assessment of severity and changes in symptomatology. Internal consistency and test-retest reliability, known-group and construct validity and sensitivity to change were evaluated. Instrument performance based on oxygen use was also assessed. RESULTS:  Data from 278 patients (79% female, mean age 60 years) were included in the analysis. 59% of patients were in WHO functional class III, 41% were on background therapy with a phosphodiesterase type-5 inhibitor and 34% used oxygen therapy at any given time. Individual item scores did not differ based on oxygen use. For all 4 domains, internal consistency reliability was very good (Cronbach’s alpha >0.80) and test-retest reliability (assessed in stable patients) was high (intra-class correlation coefficient 0.84–0.94). Correlations with CAMPHOR and SF-36 were moderate-to-high with correlations slightly lower in the cardiovascular domain than the cardiopulmonary domain. The instrument differentiated well between patients with different disease severity levels. Domain scores were sensitive to changes in clinician- and patient-reported disease severity levels. CONCLUSIONS:  The PAH-SYMPACT^® performed well - with good psychometric properties. The domain scores were reproducible, differentiated between patients of different severity, correlated with other instruments measuring similar constructs, and were sensitive to change. This PRO has the potential to become an important outcome measure in PAH.