An effective treatment already exists for many diseases. In these cases the effectiveness of a new treatment may be established by showing that the new treatment is as effective as (i.e., equivalent to) or at least as effective as (i.e., noninferior to) the old treatment. For an economic evaluation accompanying a clinical equivalence or noninferiority trial it is important to decide before the start of the study on the appropriate research question. In many cases the objective of the economic evaluation will be to show equivalence or noninferiority of the cost-effectiveness of the treatments. This has major implications for the design and analysis of the economic evaluation. In this article we propose methods for the analysis of economic equivalence and noninferiority studies that are similar to the methods applied to clinical equivalence and noninferiority trials. Furthermore, cost-effectiveness planes prove to be a valuable tool in the interpretation of the results in an economic equivalence or noninferiority trial. The concepts described in the article are illustrated using the results from an economic noninferiority trial. © 2007, International Society for Pharmacoeconomics and Outcomes Research (ISPOR).