The objective of the research was to perform a clinical practice-based analysis of how long patients remain on various antihypertensive drugs. An administrative database listing of patient baseline characteristics, drug prescriptions, and hospital admissions was used. All new users of antihypertensive drugs, > or =20 years of age, receiving a first prescription for diuretics, beta blockers, calcium channel blockers, angiotensin-converting enzyme inhibitors, or angiotensin II receptor antagonists between January 1, 2000, and December 31, 2000, were included and observed for 365 days. Persistence was defined as a duration of therapy <273 days. A total of 14,062 patients were included in the study, 39.7% of whom remained on treatment (persistent patients). Persistent patients were more likely to be older, taking other drugs for concurrent disorders, hospitalized for cardiovascular diseases, and initially prescribed angiotensin II receptor antagonists. Persistent patients accounted for 80.6% of the overall cost for antihypertensive drugs. Factors associated with drug cost were age, pattern of persistence, number of prescribed classes, and specific medication at enrollment. Measuring persistence with treatment is needed to evaluate the appropriateness and the cost-effectiveness of drug use.