OBJECTIVES: To examine the performance of various administrative claims-based algorithms with varying observation times for identifying patients with hypertension. METHODS: This retrospective analysis utilized administrative claims data linked with electronic medical records (EMR). Patients were identified in claims data using two observation time periods, 11/2010 to 12/2013 (EMR data availability) and 01/2006 to 12/2013 (entire claims data availability). Various claims-based hypertension algorithms were defined using ICD-9 diagnosis codes from medical claims and antihypertensive medications from pharmacy claims.   Sensitivity and specificity were computed for each of claims-based algorithm and the two observation time periods using hypertension diagnoses from the EMR patient problem list as the gold standard. RESULTS: From a total of 10,864 patients with integrated data, 3,272 were identified with hypertension in EMR.  When using claims in the same period as EMR availability, medical claims only based algorithms requiring one, two, or three diagnoses resulted in sensitivities of 83.3%, 75.0%, and 67.8% and specificities of 89.4%, 93.0%, and 94.6%, respectively, while the medical plus pharmacy claims based algorithms requiring pharmacy claim for an antihypertensive plus one, two, or three diagnoses resulted in sensitivities of 74.3%, 69.6%, and 64.0% and specificities of 92.7%, 94.2%, and 95.2%, respectively.  By contrast, when using the entire claims data availability, the same medical claims only based algorithms resulted in sensitivities of 91.9%, 89.4%, and 86.2% and specificities of 77.3%, 81.8%, and 84.1%, respectively, while the same medical plus pharmacy claims based algorithms resulted in sensitivities of 85.6%, 84.3%, and 82.1% and specificities of 85.3%, 86.4%, and 87.2%, respectively.  CONCLUSIONS: Claims-based algorithms for identifying hypertensive patients vary on criteria and observation time of the data.  Sensitivities are higher with medical claims only algorithms while specificities are higher when pharmacy claims are combined with medical claims.  Longer observation time results in increased sensitivities and decreased specificities.