The Centers for Medicare and Medicaid Services (CMS) Medical Evidence Report (form CMS-2728) queries providers about the timing of the patient's first nephrologist consultation before initiation of dialysis. The monitoring of disease-specific goals in the Healthy People 2020 initiative will use information from this question, but the accuracy of the reported information is unknown. We defined a cohort of 80,509 patients aged ≥67 years who initiated dialysis between July 2005 and December 2008 with ≥2 years of uninterrupted Medicare coverage as their primary payer. The primary referent, determined from claims data, was the first observed outpatient nephrologist consultation; secondary analyses used the earliest nephrology consultation, whether inpatient or outpatient. We used linear regression models to assess the associations among the magnitude of discrepant reporting and patient characteristics and we tested for any temporal trends. When using the earliest recorded outpatient nephrology encounter, agreement between the two sources of ascertainment was 48.2%, and the κ statistic was 0.29 when we categorized the timing of the visit into four periods (never, <6, 6-12, and >12 months). When we dichotomized the timing of first predialysis nephrology care at >12 or ≤12 months, accuracy was 70% (κ=0.36), but it differed by patient characteristics and declined over time. In conclusion, we found substantial disagreement between information from the CMS Medical Evidence Report and Medicare physician claims on the timing of first predialysis nephrologist care. More-specific instructions may improve reporting and increase the utility of form CMS-2728 for research and public health surveillance.