Health impact assessment (HIA) has been advanced as a means of bringing potential health impacts to the attention of policy makers, particularly in sectors where health impacts may not otherwise be considered. This article examines lessons for HIA in the United States from the related and relatively well-developed field of environmental impact assessment (EIA). We reviewed the EIA literature and conducted twenty phone interviews with EIA professionals. Successes of EIA cited by respondents included integration of environmental goals into decision making, improved planning, and greater transparency and public involvement. Reported shortcomings included the length and complexity of EIA documents, limited and adversarial public participation, and an emphasis on procedure over substance. Presently, EIAs consider few, if any,health outcomes. Respondents differed on the prospects for HIA. Most agreed that HIA could contribute to EIA in several areas, including assessment of cumulative impacts and impacts to environmental justice. Reasons given for not incorporating HIA into EIA were uncertainties about interpreting estimated health impacts, that EIA documents would become even longer and more complicated, and that HIA would gain little from the procedural and legal emphasis in EIA. We conclude that for HIA to advance, whether as part of or separate from EIA, well-formulated methodologies need to be developed and tested in real-world situations. When possible, HIA should build on the methods that have been utilized successfully in EIA. The most fruitful avenue is demonstration projects that test, refine, and demonstrate different methods and models to maximize their utility and acceptance.