This first article, in a series of two, reviews the evidence on geographic variations in the use of health care services. Large variations exist both between countries and between regions within countries. These variations cannot be explained satisfactorily by errors of data, population characteristics or health care system features. Rather, they seem to stem from the professional uncertainty surrounding the current use of health care procedures. In the absence of solid scientific knowledge regarding the relevance and the efficacy of various alternatives, different practice styles are acceptable. Geographic variations raise important questions concerning the cost of care, the health of the population and health policies. In order to deal with geographic variations and professional uncertainty, a major reassessment of health care services is warranted. Specific action strategies will be described in a second article.
