This study is an essential prerequisite to gain more insight into the complex relationship between public health and the costs of medical care. It offers a first tentative but comprehensive description of the total direct costs generated by all diseases in the Dutch population. We classified estimated direct costs of illness (39.8 thousand million guilders) by type of care, sex, age and 48 diagnostic categories for 1988. In order to estimate the costs of health care in the year 2030, we linked this information with demographic development. We were able to allocate 75% of all costs to diseases. Ranking by major disease categories revealed that mental disorders account for the highest proportion of costs (20%), followed by diseases of the circulatory system (9%), and diseases of the digestive system (8%). Costs of medical care increased significantly with age and were presumably incurred for non fatal ailments. Health care costs for men and women were almost similar. In the year 2030 the costs of dementia and diseases of the circulatory system will increase most. A reliable estimate of the costs should also take epidemiological and economic considerations into account.