The objective of this study was to validate physician billing claims against self-reported influenza vaccination to assess individual-level vaccination status. We compared responses to the Canadian Community Health Survey 1.1 (CCHS) and Ontario Health Insurance Plan (OHIP) physician billing claims and found moderate agreement. Using self-report as the gold standard, OHIP claims based on using both influenza-specific and general vaccination codes have high specificity and positive predictive value (PPV), reasonable negative predictive value (NPV), but only fair sensitivity. OHIP physician billing claims are suboptimal for ascertaining the vaccination status of individuals because many individuals receive their vaccinations outside doctor's offices, but may be used as the backbone for the creation of an immunization registry.