OBJECTIVES: Patients in intensive care units (ICUs) are often sedated for prolonged periods. The level of sedation has a direct influence on outcomes. Undersedation can lead to problems such as patient removal of the ventilator tube, or unpleasant recall after sedation, while oversedation is associated with prolonged stay in hospital. Recently, there has been increasing interest in the adequacy of sedation, with the introduction of sedation management protocols in ICUs and the development of devices to monitor sedation levels. We sought to establish the extent to which inappropriate sedation (both over and under) is reported as a problem in ICUs through a systematic review of the literature. METHODS: We conducted a systematic search of the Medline, Embase and Cinahl databases, and hand-searched ASA and ESA conferences for all studies reporting the incidence of inappropriate anaesthesia. All studies were downloaded into an electronic database. Abstracts were reviewed and data were extracted twice by independent reviewers, with any discrepancies resolved by a third person. The incidence of inappropriate sedation, including both under and oversedation, was extracted together with any information on the effects of inappropriate sedation. RESULTS: Literature searches identified 2098 citations of potential relevance to the study question. Of these, a limited number of studies reported the incidence and prevalence of inappropriate sedation, and there was variation in measurement of sedation level. CONCLUSIONS: Few studies address the incidence of inappropriate sedation within the ICU; however they indicate that inappropriate sedation does occur. Improved monitoring of sedation may have a beneficial effect on the occurrence of inappropriate sedation, with important implications for outcomes such as adverse events in patients, and length of stay and resource use in hospitals.