OBJECTIVES: To compare hospital, procedural, and ambulatory hypertension costs across eight countries (Australia, Canada, France, Germany, Italy, Spain, UK and the US) and document factors to consider when making multinational comparisons. METHODS: Data was obtained from health economics resources in each country and an international literature search. Public and private sources such as UK's Royal London NHS Trust, Personal Social Services Research Unit, and NHS Executive were used. Data tables captured four hypertension-related events: Acute Myocardial Infarct (AMI), Congestive Heart Failure (CHF), Stroke, and Renal Failure (RF). All costs were converted into US Dollars for the year 2000. RESULTS: There are considerable international variations in the hospitalization, procedural and ambulatory hypertension treatment costs. These differences can be explained partially by the source of payment, measurement of overhead, physician and hotel fees, and prevailing practice patterns, as well as whether accounting costs or actual expenditures were used. US costs appear to be higher for AMI, stroke and renal failure hospitalizations, while CHF hospitalization costs are similar across countries. The reported AMI hospitalization cost, as a percentage of the US cost, ranges from 7.1% (UK) to 43.5% (Spain). The UK and Australia appear to have the lowest hospital-related and ambulatory costs across all four events. Ambulatory costs for 1 year after an AMI, CHF, transplantation or stroke hospitalization are highest in the US. Typically the procedural and line item costs were higher in the US than in other countries. Reported CABG procedure costs ranged from 2.6% (France) to 51.8% (Italy) of US costs. CONCLUSIONS: We found wide variation in captured and reported costs for hypertension-related hospitalizations, procedures, and ambulatory care. Health services researchers should be cautious when constructing or interpreting international comparisons, particularly in differentiating between actual cost differences, differences in definition of services measured, and national practice patterns.