Introduction: Uncertainty and risk are central issues in relation to health and health care services. Healthy individuals do not necessarily fall ill, despite the presence of risk factors. Doctors, health service administrators, and patients are more inclined to choose interventions against risk factors, when information about the effects is presented in terms of relative risk reductions rather than absolute risk reductions. The aim of the study was to gain better insight into how general practitioners (GPs) perceive risk of disease, and whether this perception depends on the risk reduction being presented in absolute or relative terms. Material and methods: Questionnaires with clinical episodes were sent to 1500 Danish GPs. The GPs were randomised into four groups of 375, all of whom received the same case history with information about risk reduction achieved through medical treatment phrased in terms of either relative risk reduction, absolute risk reduction, number needed to treat, or all of the aforementioned terms of risk reduction. The GPs were asked whether they would recommend medical treatment as primary prevention, knowing the case history and expected risk reduction. Results: The GPs' attitude towards recommending medical treatment depended on the phrasing of risk reductions. Of the doctors who received all information on risk reductions, 72% would definitely or probably recommend medication, whereas 91% would recommend medication if only information about relative risk reduction was given, and 63% would recommend medication if information was given in terms of absolute risk reduction or number needed to treat. Discussion: To advise patients rationally, knowledge of the patients' preferences, as well as consideration of all available measures of risk reductions, is needed.