Webster's Dictionary defines a benchmark as 'something that serves as a standard by which others can be measured'. Benchmarking pervades the health care quality improvement literature, and benchmarks are usually based on subjective assessment rather than on measurements derived from data. As such, benchmarks may fail to yield an achievable level of excellence that can be replicated under specific conditions. In this paper, we provide an overview of benchmarking in health care. We then describe the evolution of our data-driven method for identifying an Achievable Benchmark of Care (ABC) on the basis of process-of-care indicators. Here, our experience leads us to postulate the following premises for sound benchmarks: (i) benchmarks should represent a level of excellence; (ii) benchmarks should be demonstrably attainable; (iii) providers with high performance should be selected from among all providers in a predefined way using reliable data; (iv) all providers with high performance levels should contribute to the benchmark level; and (v) providers with high performance levels but small numbers of cases should not unduly influence the level of the benchmark. An example of an ABC applied to the cooperative cardiovascular project leads the reader through the computation of an ABC. Finally, we consider several refinements of the original ABC concept that are in progress, e.g. how to approach the special problems posed by very small denominators. The ABC methodology has been well accepted in multiple quality improvement projects. This approach lends objectivity and reliability to benchmarks that have been a widely used, but until now, arbitrarily defined tool.