Our purpose was to verify some basic aspects of validation of the Unified Parkinson's Disease Rating Scale (UPDRS). One hundred and sixty-seven Parkinson's disease (PD) patients were included. Group A (n = 40) was simultaneously assessed by five raters who applied the UPDRS and other PD rating scales (PDRS). A set of timed tests, the Mini-Mental State Examination (MMSE), and the Hamilton Scale for Depression (HSD) were administered by an independent examiner. Group B (n = 127) was individually assessed through the UPDRS and the other PDRSs by one neurologist in four different hospitals. The UPDRS was administered in 16.95 +/- 7.98 min. The internal consistency was high (Cronbach's alpha = 0.96). Nevertheless, the items related to depression, motivation/initiative, and tremor were scarcely consistent. The Interrater reliability was satisfactory (all the items had k > 0.40). There was a high correlation of the UPDRS with the Hoehn and Yahr staging (rs = 0.71; p < 0.001) and some timed tests (finger tapping; arising from chair), but also with the MMSE and HSD (rs = 0.53; rs = 0.64; p < 0.001). The convergent validity with the other PDRS (Intermediate Scale and Schwab and England Scale) was very high (rs = 0.76-0.96; p < 0.001). The factor analysis identified six factors that explained 59.6% of the variance. The dimension "tremor" showed a remarkable independence. The UPDRS is a multidimensional, reliable, and valid scale, with some inconveniences derived from its internal consistency, discriminant validity, and pragmatic application.