BackgroundThe PROMIS Parent Proxy Upper Extremity Short Form 8a version 2 (PROMIS Parent Proxy UE-SF) is one of the most commonly used self-assessment questionnaires for evaluating function in children with congenital upper extremity anomalies. However, this English questionnaire is difficult for Thai parents to complete. The purpose of this study is to translate the PROMIS Parent Proxy UE-SF into Thai and test its reliability and validity.MethodsThe PROMIS Parent Proxy UE-SF was translated into Thai using FACIT translation methodology. This version and the Thai version of the Michigan Hand Questionnaire (Thai-MHQ) were used to evaluate 30 Thai children with different types of congenital upper extremity anomalies. The reliability and validity of the Thai-PROMIS Parent Proxy UE-SF were evaluated by test-and-retest with the intraclass correlation coefficient (ICC) and Cronbach’s alpha coefficient. Correlations between the Thai-PROMIS Parent Proxy UE-SF and Thai-MHQ were analysed by Pearson’s correlation coefficients.ResultsThe children’s mean age was 4.47 ± 2.08 years (range 1–9 years). The main diagnoses included thumb duplication (11 children), syndactyly (4 children)4, congenital trigger thumb (3 children) and obstetric brachial plexus palsy (3 children). The children’s parents completed the questionnaires, taking 164.23 ± 22.58 s for the Thai-PROMIS and 337.8 ± 49.37 s for the Thai-MHQ. The test-retest reliability of Thai-PROMIS evaluated by ICCs, was 0.9909 (good reliability), and the Cronbach’s alpha of all items was 0.923. The Pearson’s correlation coefficient between the Thai-PROMIS and Thai-MHQ showed a strong correlation with Domain 2 (activities of daily living, r = 0.7432) and a moderate correlation with the overall Thai-MHQ score (r = 0.699).ConclusionsThe Thai-PROMIS Parent Proxy UE-SF is a valid, reliable and easy-to-use patient-reported outcome measure for assessing function in children with congenital upper extremity anomalies.