BACKGROUND: Incremental cost-effectiveness ratios (ICERs) represent the cost per unit of effectiveness of switching to a more costly and more effective option. In reporting results for cost-effectiveness (CE) analyses, options that are strictly dominated are ruled out and no ICERs should be reported. Additionally, some options may be ruled out by extended dominance (i.e., there is a linear combination of two options that dominates an option not otherwise excluded by strict dominance). In order to plot the CE efficiency frontier both strictly and extendedly dominated options must be excluded. Calculating strict dominance (e.g., in Excel) is straightforward. However calculating extended dominance is more complex. METHODS: We present a method to exclude extendedly dominated options using an ICER matrix. To form an ICER matrix all options are rank ordered by cost. For a CE analysis with N options, the ICER matrix is an N x N-1 sized table, where the first column represents the ICER from the least costly option to each more costly option, the second column represents the ICER from the second least costly option to each more costly option, etc.. Negative ICERs, representing strictly dominated options, are excluded from the table. Extended dominance is established by calculating whether the ICER for a non-strictly dominated option is greater than the ICER for at least one more costly option. If so, the option is rule out by extended dominance, otherwise not. We show how to perform the required calculations in Excel and how to graphically plot the CE efficiency frontier once all dominated and extendedly dominated options have been excluded. CONCLUSIONS: Strictly dominated and extendedly dominated options must be ruled out in order to plot the CE efficiency frontier. The ICER matrix is a systematic method to rule out strictly and extendedly dominated options.