['Delirium in critically ill patients is associated with increased length of hospital stay, mortality and costs, and may lead to long-term cognitive impairment. It is often overlooked by clinicians if structured observation is not performed routinely. A national Norwegian survey reported that systematic screening and assessment of delirium were never or seldom performed. The purpose of this study was to test the usefulness of the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) and to describe the incidence of delirium in critically ill patients at two Norwegian hospitals.', 'We conducted a two-site, prospective, descriptive study including patients between 18 and 80 years, intubated or mask ventilated at admission, with an ICU stay >\u200948\u2009h. The CAM-ICU was scored three times daily. In addition, illness severity, sedation level, pain assessment, drug use and other treatment factors were systematically assessed.', 'Total ICU stays of 139 patients were studied and covered 958 patient days. The incidence of delirium was 23%. Thirty per cent of the patients representing 407 patient days were unable to be assessed at any assessment, mainly due to deep sedation. The patients were delirium and coma free in 45.9% of total days.'] Does the incidence of delirium in Norwegian intensive care units ; deep sedation make assessment difficult?