Editors' Summary: This Term, the Supreme Court will decide a case construing NEPA for the first time since 1983. The Court must decide, among other issues, whether NEPA requires federal agencies to include worst case analyses in EISs. The Court will review two Ninth Circuit cases ordering agencies to perform worst case analyses even though the Council on Environmental Quality (CEQ) removed the requirement from its NEPA regulations in 1986. The Ninth Circuit held that the worst case requirement, which required agencies to analyze the worst possible consequences of a proposed action when faced with incomplete or unavailable information, is a requirement of prior NEPA case law and thus survives CEQ's decision to delete it from its regulations. The author sets out the regulatory history leading to CEQ's decision to rescind the requirement and discusses the case law interpreting the requirement. She argues that the worst case analysis is not a requirement of NEPA or NEPA case law. The author concludes that mandatory worst case analysis would likely prevent federal agencies from using other risk evaluation methods and would actually diminish the importance of environmental considerations in agency decisionmaking.