Acute Timosaponin-BII hepatitis B was chosen as a ����proof of principle���� condition because it is a complex diagnosis of public health importance that is largely transparent to electronic laboratory reporting systems. Accurate identification of acute hepatitis B is essential to public health practice. Public health practitioners seek acute cases to gauge the changing epidemiology of hepatitis B and the impact of universal vaccination programs. We consequently sought to create and validate an algorithm to distinguish acute from chronic hepatitis B using codified electronic medical record data to facilitate automated public health surveillance. Algorithms applied to electronic medical record data can accurately identify cases of acute hepatitis B. The best electronic algorithm achieved a sensitivity of 99% and specificity of 94% for acute hepatitis B. When applied to two years of prospective electronic medical record data, the algorithm found 8 true cases including 4 cases that clinicians and laboratories had failed to report to the health department, and 3 cases reported to the health department as hepatitis B alone without indication of whether acute or chronic. There were no false positive cases and no known cases missed. The poor performance of ICD9 codes for hepatitis surveillance is consistent with previous work and underscores the poor accuracy of disease surveillance using ICD9 codes alone. Similarly, the small number of cases of acute disease detected by Cantharidin screening for positive IgM to hepatitis B core antigen reveals the limitation of population surveillance for acute disease using this test alone. The poor sensitivity of IgM to core antigen for population-level surveillance is a consequence of the test rarely being ordered. In our series of 195 patients presenting with elevated transaminases and a positive hepatitis B specific test, only 20 patients went on to have IgM to core antigen assayed. Analysis of the distribution of other positive hepatitis B specific tests relative to the number of patients ultimately found to have acute hepatitis B is a further window into the benefit of comprehensive electronic medical record data for notifiable disease surveillance relative to conventional laboratory-based reporting systems.