INTRODUCTION: Little is known about cross-national comparisons of the persistence of antihypertensive medication treatment, trends in persistence, and factors associated with persistence. The aim of this study was to describe and compare patterns ouse of antihypertensive drugs in a population of elderly patients in the United States (Pennsylvania), Canada (British Columbia) and the Netherlands. METHODS: A retrospective cohort study of Medicare enrollees in a state pharmacy assistance programme inPennsylvania (USA), residents from British Columbia (Canada) and residents from the Netherlands registered in the PHARMO database was conducted. Each population included patients 65 years and older who were initiated on blood pressure-lowering treatmentbetween 1 January 1998 and 31 December 2003 and who had continuous follow-up for at least 365 days. In these populations, the proportion of patients with at least 180 consecutive days without medication available (non-persistence) were identified as were predictors of non-persistence using Cox proportional hazards. RESULTS: A total of 9664 Medicare enrollees (USA), 25 377 residents from British Columbia and 24 603 residents from the Netherlands were evaluated. During the first year after the initiationof treatment, the percentage of patients with at least 180 days without medication was 23.3% in Pennsylvania, 23.4% in British Columbia and 24.0% in the Netherlands. After 6 years, these percentages increased to 41.1, 36.3 and 38.2%, respectively. Factors associated with non-persistence were different between the three countries. CONCLUSION: Despite differences in factors associated with persistence, non-persistence patterns are strikingly similar in all three populations. This suggests that the problem of non-persistence transcends international boundaries.