The primary objective of this study was to assess the intra-rater reliability of the motor section of the Unified Parkinson's Disease Rating Scale (UPDRS-III) in patients with advanced Parkinson's disease (PD). The secondary objective was to assess the intra-rater reliability of standard timed motor tests and dyskinesia scales to determine the necessity of multiple baseline core evaluations before surgery for PD. We carried out two standardized preoperative core evaluations of patients with advanced PD scheduled to undergo deep brain stimulation. Patients were examined in the defined off and on conditions by the same rater. UPDRS-III, timed tests, and dyskinesia scores from the two evaluations were compared using Wilcoxon Signed Ranks tests and intraclass correlation coefficients (ICC). Differences in UPDRS-III scores for the two visits were clinically and statistically nonsignificant, and the ICC was 0.9. Similarly, there were no significant differences in timed motor tests or dyskinesia scores, with a median ICC of 0.8. The results indicate that previous findings of high test-retest reliability of UPDRS-III in early untreated PD patients can now be extended to those with advanced disease complicated by motor fluctuations. In addition, test-retest reliability of dyskinesia scales and timed motor tests was high. Taken together, these findings challenge the need for multiple baseline assessments as currently stipulated in core assessment protocols for surgical intervention in PD.