Conventional wisdom teaches us that cost-benefit analysis (CBA) and the precautionary principle conflict. CBA proponents consider precaution incoherent and irrational, while precautionary principle fans see CBA as a threat to environmental protection. Both sides, however, see these two concepts as conflicting. This Article questions the conventional view. It finds no conflict between the precautionary principle, properly understood, and the mere idea of taking costs and benefits into account in choosing environmental standards. The reasoning underlying this conclusion illuminates both concepts. Having revealed the theoretical possibility of precautionary CBA, it uses a case study of the climate disruption issue to begin fleshing out what precautionary CBA might look like.