There has been much recent debate in the health economics literature as to the (near) equivalence of cost-benefit analysis (CBA) and cost-effectiveness analysis (CEA). The aim of this paper is to demonstrate that whether such a (near) equivalence exists depends on whether one defines economic evaluations as 'CBA' or 'CEA' on the basis of either what is measured or what question the analyst is seeking to answer. The former basis of definition is popular within the 'decision science' approach to economic evaluation, but does not seem to have any theoretical support. If the latter, more theoretically correct, basis is accepted, there is no longer a case for the (near) equivalence of CBA and CEA.