The clinical indicator is a tool used to monitor the quality of health care. Its use in the Intensive Care Unit (ICU) is desirable for many reasons: the maintenance of minimum standards, the development of best practice and the delivery of cost-effective health care. The utility of clinical indicators in ICU is limited by the lack of universal, robust, transparent, evidence-based and risk-adjusted measures of quality, and the difficulties in defining "quality care" and "good outcome". Monitoring of adverse events, system descriptors, and resource indicators is valuable but they have a limited relationship to the quality of care. ICU mortality prediction models provide a global measure of quality and, despite their inherent deficiencies, remain one of the most robust and useful clinical indicators.