Delirium is an acute, reversible and fluctuating central nervous system dysfunction with an organic cause, and is associated with substantial morbidity and mortality. Many recent studies have shown that delirium is highly prevalent in the Intensive Care Unit (ICU) population. Despite its seriousness; delirium in the ICU is under recognized by bedside nurses. OBJECTIVE: To determine if routine bedside nurse-patient interactions enable the detection of delirium. METHOD: We performed a single center observational study, in a 12 bed general Intensive Care Unit. Bedside nurses were asked to assess patients for delirium during routine patient care throughout their shift. This assessment was then compared to an independent assessment using the Confusion Assessment Method - ICU (CAM-ICU) performed by a nurse trained in this delirium detection tool. RESULTS: We analysed the results of 35 matched assessments performed on 35 patients. The presence of delirium was identified by the bedside nurse in 27 of CAM-ICU delirium positive assessments, whereas the absence of delirium was identified by the bedside nurse in 92 of CAM-ICU delirium negative assessments. CONCLUSION: There was a significant discrepancy between the ICU bedside nurses assessment of delirium and the independent formal delirium assessment utilizing the CAM-ICU. We concluded that routine bedside nursing patient interaction do not reliably detect delirium in a critically ill patient.