OBJECTIVES: Both English and Chinese versions of the 8-item Parkinson's Disease Questionnaire (PDQ-8) have demonstrated validity and reliability. However, the measurement equivalence of these two versions is not known. The purpose of this study was to test the differential item functioning (DIF) between the English and Chinese versions of the PDQ-8. METHODS: Data collected using the English (N=173) and Chinese (N=117) versions of the PDQ-8 from patients with Parkinson's disease in Singapore were analyzed. DIF was detected using both an ordinal logistic regression model and a generalized partial credit model. RESULTS: No DIF was detected for any of the 8 items of the PDQ-8 between the English and Chinese versions. The only item with suspicious DIF was “Due to having Parkinson's disease, how often during the last month have you felt unable to communicate with people properly?” Chinese-speaking patients responded more positively than English-speaking patients to this question; however, this difference was insignificant, either statistically or according to pre-defined effect size of minimal importance. CONCLUSION: The English and Chinese versions of the PDQ-8 appear equivalent in measurement, thus data colleted by these two versions can be pooled for data analysis without statistical adjustment.