The controversy over patients’ access to stem cell interventions is familiar to scholars of the drug regulatory system and the politics of evidence-based medicine. What counts as evidence of a biomedical intervention's safety and effectiveness? Who should define and assess safety and effectiveness, and how? In the first section of the paper we describe the types of stem cells that may be therapeutically effective. We then describe how the US Food and Drug Administration asserted regulatory authority over certain stem cell interventions and the legal challenge to the agency's actions. Next, we place the debate about patients’ access to stem cell interventions in the broader context of efforts in the US to promote and implement health technology assessment and the debate about standards of evidence. We then review several proposed initiatives to get stem cell and other new biomedical interventions into the clinic faster and consider the extent to which these policies can resolve the underlying conflicts about evidentiary standards for clinical use. Finally, we consider whether efforts to expedite access to biomedical technologies may undermine countervailing efforts to improve the safety and effectiveness of stem cell interventions.