Global climate change is receiving worldwide attention because of its anticipated impacts on the Earth's physical and biological systems. Through its effects on natural and human environments, climate change will likely impact economic viability and human health and well-being. The impact of climate change on human health is likely to be complex and significant, including effects on cancers, cardiovascular and respiratory disease, food-, water-, and vector-borne diseases, heat-related illness, mental and social well-being, nutrition, trauma, and vulnerable demographic sectors. Most assessments predict that these effects will disproportionately affect the poor, the elderly and the young, especially those living in Africa and Southeast Asia, where environmental conditions are poor, health infrastructure is weak and the burden of disease is great. Enormous efforts are underway to plan and finance climate change adaptation programs within national governments (including multiple U.S. agencies), United Nations organizations and private philanthropies. However, these endeavors are proceeding with a relatively poor understanding of the nature and magnitude of probable effects of climate change on health. The National Institutes of Health (NIH) already funds a portfolio of projects that are indirectly related to the concerns posed by global climate change. At the NIH, we have recently established an agency-wide planning group to assess the research questions in health and medicine that climate change presents, to link this agenda to parallel activities across other agencies of the U.S. Government (USG), and to advance a NIH research agenda in this area.