Intensive care units (ICUs) share the problems experienced by the health care system at large. Various approaches to define and manage the quality of care patients receive in the ICU have been proposed. Performance measurement involves the collection of data to evaluate an ICU's performance against itself (over time), other ICUs, or other appropriate benchmarks. Successful performance assessment requires the quantification of relevant indexes of performance. Although these indexes are increasingly being developed, it will be some time before widely recognized, validated systems are available.