There are growing demands for governments to carry out human rights impact assessments prior to adopting and implementing policies. This article outlines a preliminary human rights impact assessment methodology, using the right to the highest attainable standard of health as the case study. The authors recommend a mainstreaming approach, which involves integrating human rights into existing impact assessment methodologies. Accordingly, they identify considerations that, from a human rights perspective, governments should incorporate into existing impact assessment methodologies in order to comply with their legal obligations to realize human rights. To test the mainstreaming methodology, the authors propose integrating the right to the highest attainable standard of health into health impact assessment.