BACKGROUNDDelirium is a syndrome that occurs in all age groups and in many clinical departments, and is most common in intensive care units. It is an emergency, in the overlapping fields of somatic medicine, neurology and psychiatry. Delirium occurs suddenly, dramatically, and requires a quick reaction, recognition and treatment. There are only a small number of studies that have reported delirium after a stroke. In our study, the goal was to determine the cognitive functionality of patients with delirium after a stroke. SUBJECTS AND METHODSThis is a prospective study in which a group of 100 delirium patients in the acute phase of a stroke were evaluated for cognitive function. The control group consisted of the same number of patients with acute stroke who were not diagnosed with delirium. Neurological, neuropsychiatric and neuropsychological tests were performed in all patients at five different time periods. In these time periods, all patients were evaluated: Glasgow Coma Scale; Delirium Assessment Scale; The American National Institutes of Health Scale Assessment; Information-Memory-Concentration test; Dementia Score; Mini-Mental Test. The findings of computed tomography of the brain and magnetic resonance imaging of the brain were interpreted by a radiologist who was not familiar with the goals of this study. RESULTSCognitive functioning of delirious patients is statistically significantly worse after three and six months, and one year from stroke compared to those without delirium. There is no statistically significant difference in cognitive functioning between delirious patients in relation to gender, age, location and type of stroke and patients without delirium throughout one year from stroke. There is no significant difference in cognitive functioning between delirious patients during one year from stroke in relation to severity and type of delirium, and statistically significantly higher degree of cognitive dysfunction has those older than ≥65 years. CONCLUSIONSDelirium significantly reduces the cognitive functioning of patients after a stroke.