Purpose: PROMIS is becoming the most commonly utilized patient-reported outcome measure (PROM) in adult orthopaedics, but its adoption has lagged in pediatrics. Limited baseline data exists in pediatric-specific orthopaedic diagnoses. The objective of this study was to determine baseline PROMIS scores in patients with idiopathic scoliosis and to evaluate for correlations with the SRS-22. Methods: This was a retrospective analysis of prospectively collected data from six tertiary care pediatric hospitals between July 2016 and July 2018. Patients with a diagnosis of idiopathic scoliosis, adequate radiographs for measurement and completion of PROMIS and SRS-22 questionnaires from the same visit were included. Only the first visit during the study period was included for each subject. Post-operative patients were excluded. Spearman correlations were performed between four PROMIS domains (Pain interference [PI], Mobility [M], Peer Relationships [PR] and Upper Extremity [UE]) and SRS-22 domains. PROMIS scores are calibrated such that 50 is the median value in a population and 10 points is equivalent to one standard deviation. Results: 986 patients with a mean age of 14.6 years were included, 79.8% of which were female. The mean major curve was 33.0° (range: 10–102). The major curve was thoracic in 56.5%, thoracolumbar in 24.4% and lumbar in 19.1% of subjects. The mean PROMIS domain scores were: Pain Interference 44.5 (IQR 17.7); Mobility 52.7 (IQR 12.5); Peer Relationships 55.7 (IQR 15.0); Upper Extremity 53.4 (IQR 7.7). Correlations existed between PROMIS Pain Interference and SRS-22 pain (r = 0.704, p < 0.001) and PROMIS Mobility and SRS-22 function (r = 0.53, p < 0.001). Significant ceiling effects existed in SRS-22 Function (29.9%), Pain (19.2%) and Satisfaction (30.3%) but only for PROMIS Peer Relationships (42.1%). Conclusions: PROMIS domain scores for patients with AIS are within normal population limits. PROMIS correlates well with SRS-22 in overlapping domains, and fewer domains demonstrate a ceiling effect. There was no relationship between the magnitude of scoliosis and PROMIS domain scores. Level of evidence: II.