Under the Clean Air Act, the U.S. Environmental Protection Agency (EPA) is required to determine the stringency of the National Ambient Air Quality Standards (NAAQS), arguably the most important federal environmental program, without considering the costs of achieving these standards. Instead, it must rely exclusively on health-related criteria. This Article argues that health-based standards, which are one of the principal approaches to setting the stringency of environmental requirements in the United States, exhibit two serious pathologies: the stopping-point problem and the inadequacy paradox. The stopping-point problem arises because there is no coherent, defensible way for EPA to set the permissible level of pollution based on health considerations alone. Moreover, contrary to the commonly accepted view, the NAAQS have generally been set at levels that are less stringent than those that would result from the application of cost-benefit analysis, giving rise to the inadequacy paradox. We urge a reinterpretation of the Supreme Court’s important decision in Whitman v. American Trucking Associations to avoid the inadequacy paradox.