Purpose: This study aimed to validate the PROMIS Pediatric item bank v2.0 Peer Relationships and compare reliability of the full item bank to its short form, computerized adaptive test (CAT) and the social functioning (SF) subscale of the Pediatric Quality of Life Inventory (PedsQL™). Methods: Children aged 8–18 (n = 1327), representative of the Dutch population completed the Peer Relationships item bank. A graded response model (GRM) was fit to the data. Structural validity was assessed by checking item-fit statistics (S-X 2 , p < 0.001 = misfit). For construct validity, a moderately strong correlation (> 0.50) was expected between Peer Relationships and the PedsQL SF subscale. Cross-cultural DIF between U.S. and NL was assessed using logistic regression, where an item with McFadden’s pseudo R 2 > 0.02 was considered to have DIF. Percentage of participants reliably measured was assessed using the standard error of measurement (SEM) < 0.32 as a criterion (reliability of 0.90). Relative efficiency ((1-SEM 2 )/n items ) was calculated to compare how well the instruments performed relative to the amount of items administered. Results: In total, 527 (response rate: 39.7%) children completed the PROMIS v2.0 Peer Relationships item bank (n items = 15) and the PedsQL™ (n items = 23). Structural validity of the Peer Relationships item bank was sufficient, but one item displayed misfit in the GRM model (S-X 2 < 0.001); 5152R1r (“I played alone and kept to myself”). The item 733R1r (“I was a good friend”) was the only item that displayed cross-cultural DIF (R 2 = 0.0253). The item bank correlated moderately high (r = 0.61) with the PedsQL SF subscale Reliable measurements were obtained at the population mean and > 2SD in the clinically relevant direction. CAT outperformed all other measures in efficiency. Mean T-score of the Dutch general population was 46.9(SD 9.5). Conclusion: The pediatric PROMIS Peer Relationships item bank was successfully validated for use within the Dutch population and reference ...