An analysis was performed of the 1-year continued use of various antihypertensive agents in a health maintenance organization following the 2002 publication of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT). Computer-stored information was used from the health maintenance organization's prescription information system. Only patients newly started on antihypertensive medications in 2001 and the calendar year following the ALLHAT publication were analyzed. Patients were considered to be persistent with their first prescribed antihypertensive drug class if they obtained at least one refill for the same class of antihypertensive agents on or within 3 months of the end of the 1-year follow-up period. The overall 1-year continuation rate decreased from 2001 to 2003. However, the continuation of thiazide-type diuretic use after ALLHAT (2003) was higher than that before ALLHAT (2001) (p=0.004), whereas the continuation rate was lower for all other drug classes. We provide data to suggest that evidence from randomized trials is one factor influencing the continued use of antihypertensive medication.