Our analyses used 166 weeks of data from the 2003-04 through the 2007-08 influenza seasons obtained from three influenza surveillance systems used to monitor national and regional influenza trends. Data included five influenza seasons from 2003-04 through the 2007-08 influenza season. There was a strong temporal association among rates from each surveillance system ( Figure 1 ). Scatter plots of Google Flu Trends and CDC ILI Surveillance with the reference standard data showed high linear correlations ( Figure 2 and Figure 3 ). Pearson's correlation coefficient describing the strength of association between Google Flu Trends with CDC Virus Surveillance was 0.72 (95% CI: 0.64, 0.79) ( Figure 2 and Table 1 ). The strength of association between CDC ILI Surveillance and CDC Virus Surveillance was higher, with a correlation coefficient of 0.85 (95% CI: 0.81, 0.89) ( Figure 3 and Table 1 ). Google Flu Trends, which had been fit to CDC ILI Surveillance, was highly correlated to that surveillance data (R = 0.94; 95%CI: 0.92, 0.96).