The concept of cost-effectiveness is illustrated graphically on the CE plane. Strategies are represented according to their effectiveness (e) and cost (c) relative to those of some reference standard. A straight line with slope K passes through the origin, where K is the maximum acceptable cost-effectiveness ratio. Strategies plotted to the right of line K are cost-effective, while those plotted to the left are not. Furthermore, the most cost-effective of two or more mutually exclusive alternatives is that plotted the greatest distance to the right of K. The CE plane can be used to resolve ambiguities about the meaning of cost-effectiveness and to illustrate its relevance to medical decision making.