The simulation model "Prevent" estimates the effect on mortality of changes of exposures to risk factors taking the multifactorial nature of the associations between risk factors and diseases, time dimensions, and demography into account. The objective of the study is to compare the actual development of ischaemic heart disease mortality in Danmark from 1982 to 1991 with the estimated mortality based on the development of four risk factors. The sources of data used in the study are national population data and mortality rates and prevalences of risk factors from population surveys (Glostrup Population Studies). Relative risk estimates are those implemented in the Dutch version of Prevent based on international literature. The risk factors are: tobacco smoking, hypertension, cholesterol, and alcohol consumption. Results are given for ages below 65 years. The pronounced decline in mortality of ischaemic heart disease in Denmark cannot be foreseen by the model based on the development of the associated risk factors. However, the combined trend of risk factors for the last 10 to 15 years is only modest and does not indicate the dramatic decline in mortality. Prevent is too simple to make a satisfactory forecast of mortality, which however, is not the main purpose of the model. By comparing the development of a reference and an intervention population the effects of unknown factors are to some extent eliminated and the model may therefore give a good impression of the benefits of preventive interventions.