Given the limited resources for preventive care, policy-makers need to consider the efficiency/cost-effectiveness of preventive measures, such as drugs and vaccines, when allocating preventive care resources. However, in many settings only limited information on lifetime costs and effects of preventive measures exists. Therefore, it seems useful to provide policy-makers with some simplifying rules when allocating preventive care resources. The purpose of this article is to investigate the relevance of risk and severity of the disease to be prevented for the optimal allocation of preventive care resources. The report shows - based on a constrained optimization model - that optimal allocation of preventive care resources does, in fact, depend on both factors. Resources should be allocated to the prevention of diseases with a higher probability of occurrence or larger severity. This article also identifies situations where preventive care resources should be allocated to the prevention of less severe disease.