The level and distribution of health risks in a society is substantially influenced by measures of various policies, programmes or projects. Risk assessment can evaluate the nature, likelihood and severity of an adverse effect. Health impact assessment (HIA) provides similar function when used as a powerful tool for the evaluation of potential health consequences of planned measures. It is often discussed whether HIA is not just another term or form of risk assessment and what is their relation. Our aim is to discuss similarities and differences between the two methods so as to clarify their relationship. The experiences accumulated during the preparation of several case studies in a large scale international project (RAPID) are used for argumentation and formulation of recommendations on how risk assessment can be systematically integrated into the HIA process. Risk assessment uses well standardised scientific methods to characterise the probability and magnitude of harm caused by a hazard, preferably in a quantitative manner. In turn, HIA is a process to assess future impacts of recent proposals and is dominated by qualitative evaluation. It makes a projection for a future scenario rather than assessing a present situation. As part of this process, however, methods applied in risk assessment are used. Risk assessment typically characterises relation of a well-defined risk factor to a well-defined health outcome. Within HIA usually several individual risk assessments are needed in the risk appraisal phase to describe effects of various factors on different health outcomes. Consequently, HIA is typically led by a large, preferably intersectoral steering group with representatives of communities at risk. Risk assessment, in contrary, is mainly a licensed scientific process completed by licensed experts and lacks participatory approach. According to our findings, to be able to manage the analysis of the complex impact structure of various planned measures in HIA, the comprehensive assessment of health effects requires the analysis of the full impact scheme and must follow each level of the causal chain from the proposal through related health determinants and risk factors to health outcomes. The stepwise analysis, systematic prioritization and consideration of horizontal interactions between the causal pathways make it feasible to use widely recognized risk assessment methods in the HIA process, even in the most demanding cases of policy HIAs.