Intensive and critical care in the intensive care unit (ICU) is often associated with ICU delirium and post-ICU dementia, regardless of the nature of the primary disease or insult. Optimal practical management of ICU delirium including its screening, prevention, and treatment, is an integral part of the current recommendations for optimal ICU care, but there are large gaps in the knowledge about the optimal and most effective prevention and treatment of this complication. Information on the actual implementation of these recommendations in the Czech Republic is lacking. The diagnosis of delirium is particularly challenging in neurointensive care patients (due to overlap with symptoms of primary brain lesions) and in a paediatric population. A complementary multicentre observational 4-year follow-up study, performed in an adult neurointensive/critical care stroke cohort and in a paediatric intensive/critical care cohort in centres following currently recommended preventive measures (Delusion-deep-cz) will investigate the incidence of ICU delirium and post-ICU dementia and their modifiable and non-modifiable predisposing and precipitating risk factors. Objectives are to determine the optimal methods for diagnostic screening of these complications and for the differential diagnosis of conditions mimicking delirium (non-convulsive epileptic state) or symptoms hindering its diagnosis (aphasia), and to study the association between sleep disturbances and ICU delirium to verify the role of sleep in the pathophysiology of delirium.