Although previous studies have shown that hypertension management has improved in Canada during the past decade, this study was designed to determine whether these changes were temporally related to initiation of the Canadian Hypertension Education Program in 1999. Antihypertensive prescription rates in Ontario were compared using time series analyses before and after 1999 in 2 Ontario cohorts: all hypertensives prescribed therapy (using the Intercontinental Medical Statistics CompuScript Database) and all elderly hypertensives without diabetes prescribed therapy (using linked administrative databases including the Ontario Drug Benefit Database). Between January 1998 and December 2003, &280 million prescriptions for antihypertensive agents were filled in Ontario, and total antihypertensive prescriptions increased by 58% annually; time series analyses confirmed that the prescribing rates for total antihypertensives, thiazide diuretics, beta-blockers, and calcium channel blockers increased significantly after 1999, even after adjustment for the temporal trends in the pre-1999 data. In the 166,018 nondiabetic individuals over age 65 who were newly treated for hypertension in Ontario between July 1994 and March 2002, changes in prescription rates for total antihypertensive drugs, angiotensin-converting enzyme inhibitors, beta blockers, and calcium channel blockers occurred in directions that were consistent with guideline recommendations and were statistically significantly related to the initiation of the Canadian Hypertension Education Program. The substantial changes in prescription rates for guideline-recommended antihypertensive drug classes in elderly Ontarians without diabetes and the general Ontario population seen in the past decade are temporally related to the initiation of the Canadian Hypertension Education Program.