BACKGROUND: The Movement Disorder Society (MDS)-sponsored revision of the Unified Parkinson's Disease (PD) Rating Scale (UPDRS) (MDS-UPDRS) has been developed and is now available in English. Part of the overall program includes the establishment of official non-English translations of the MDS-UPDRS. We present the process for completing the official Japanese translation of the MDS-UPDRS with clinimetric testing results. METHODS: In this trial, the MDS-UPDRS was translated into Japanese, underwent cognitive pre-testing, and the translation was modified after taking the results into account. The final translation was approved as Official Working Draft of the MDS-UPDRS Japanese version and tested in 365 native-Japanese-speaking patients with PD. Confirmatory analyses were used to determine whether the factor structure for the English-language MDS-UPDRS could be confirmed in data collected using the Official Working Draft of the Japanese translation. As a secondary analysis, we used exploratory factor analyses to examine the underlying factor structure without the constraint of a pre-specified factor organization. RESULTS: Confirmatory factor analysis revealed that Comparative Fit Index for all Parts of the MDS-UPDRS exceeded the minimal standard of 0.90 relative to the English version and therefore Japanese translation met the pre-specified criterion to be designated called an OFFICIAL MDS TRANSLATION. Secondary analyses revealed some differences between the English-language MDS-UPDRS and the Japanese translation, however, these differences were considered to be within an acceptable range. CONCLUSIONS: The Japanese version of the MDS-UPDRS met the criterion as an Official MDS Translation and is now available for use (www.movementdisorders.org).