Delirium is common in patients who are critically ill, often resulting in extended hospital stays and increased mortality and morbidity. There are several subtypes of delirium, which are often undiagnosed and untreated, resulting in suboptimal patient outcomes. This article examines delirium in patients in the intensive care unit, including its signs and symptoms, incidence, causes and subtypes. It outlines the assessment of delirium and the pharmacological and non-pharmacological interventions that can be used to manage the condition, as well as describing the optimal prevention measures.