BACKGROUND: The objective of this study was to document changes in the prevalence and treatment of hypertension in Halifax County from 1985 to 1995 in an effort to observe, at the population level, the consequences of the availability of new antihypertensive medications. METHODS: The study population comprised a random sample of Halifax County residents, aged 25-64 years, who responded to the 1985 and 1995 surveys of the Halifax County MONICA Project and residents who responded to the Nova Scotia Health Survey conducted in 1995. Data from the two 1995 surveys were pooled. Information on hypertension awareness and use of medication were obtained through questionnaires, and blood pressure was measured according to a standard protocol, using phase I and V of Korotkoff sounds as respective markers for systolic and diastolic pressures. Uncontrolled hypertension was defined as a systolic pressure of 140 mm Hg or greater and a diastolic pressure of 90 mm Hg or greater. Changes in the prevalence of hypertension, prescribing trends and medication costs were examined, and the association between the type of antihypertensive treatment and characteristics of the respondents with self-reported hypertension was investigated by multivariate logistic regression. RESULTS: Of the 917 people interviewed in 1985 and the 1338 in 1995, 274 (29.9%) and 356 (26.6%), respectively, reported a history of hypertension. When age was controlled for, the proportion of respondents reporting hypertension did not differ between survey years or between men and women. The proportion of treated respondents who had uncontrolled hypertension increased between 1985 and 1995, from 32.6% to 57.4% among men and from 38.0% to 42.6% among women. An increase was seen in the use of calcium-channel blockers (from 2.1% to 19.7%) and angiotensin-converting-enzyme inhibitors (from 5.2% to 25.4%); the proportion of patients receiving combination therapy or diuretics decreased (from 39.6% to 15.6% and from 31.3% to 17.2% respectively). These changes were associated with an increase in the average daily cost of medication from $0.48 to $0.85 per patient. INTERPRETATION: The shift to new antihypertensive drugs was not associated with improved blood pressure control, but it was associated with an increase in average medication costs per patient. Uncontrolled hypertension remains a public health problem.