A number of factors may affect the cost effectiveness of treatments and can cause this to vary by location. These factors include the patient population, relative price levels, clinical practice patterns and incentives to health professionals and institutions such as hospitals. This paper illustrates these issues by assessing the relative cost effectiveness of 3 nonsteroidal antiinflammatory drugs (NSAID), with different levels of gastrointestinal side effects, in 3 countries. We conclude that the relative cost effectiveness of drugs is not only dependent on drug price but may also vary by country.