BKGROUND: No studies have tested the validity of the Copenhagen Hip and Groin Outcome Score (HAGOS) using modern test theory, across different cultures and languages. OBJECTIVE: To validate the Danish, English and Norwegian versions of HAGOS and its six subscales (Symptoms (S, Item 1-7), Pain (P, Item 1-10), activities of daily living (Item 1-5), Sport and recreation (Sport/rec, Item 1-8), Participation in physical activity (item 1-2) and quality of life (item 1-5)) by evaluating differential item functioning (DIF) and measurement invariance across the three language versions in male multidirectional team athletes with groin pain. Second, to modify subscales depending on goodness-of-fit to the item response theory models and calculate conversion tables if language DIF was observed. METHODS: We included individual responses to the Danish (n=157), English (n=146) and Norwegian (n=149) language versions of HAGOS from 452 athletes (median age 24 years old, range 20-28) with groin pain. Overall fit, model fit, individual item fit, local response dependence and measurement invariance was examined using confirmatory factor analysis and graphical Rasch models. RESULTS: The removal of seven misfitting items (S2, P1, P2, A4, SP1, SP5, Q3) resulted in 6 HAGOS subscales with acceptable psychometric properties. For the Symptoms, Pain and Sports subscales evidence of DIF was disclosed between the three different language-versions of HAGOS and conversion tables were created. CONCLUSIONS: A revised HAGOS derived using modern test theory provides valid measurements for male multidirectional athletes with groin pain across different cultures and languages. Conversion tables must be applied to compare HAGOS scores from Danish, Norwegian and English language versions.